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Agriculture Handboo-k No. 134 

QUEFNS BOROUGH 
PUBLIC LIBRARY 

AUG 3 1976 

i'epository Document 



MAPLE SIRUP 
PRODUCERS 
MANUAL 




UNITED STATES DEPARTMENT OF AGRICULTURE • AGRICULTURAL RESEARCH SERVICE 



From the collection of the 



n 
m 



Prejinger 
V Jjibrary 

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San Francisco, California 
2008 



AGRICULTURE HANDBOOK NO. 134 



MAPLE SIRUP PRODUCERS MANUAL 



By 

c. o. waiits 

and 
Claude H. Hills 



Agricultural Research Service 
UNITED STATES DEPARTMENT OF AGRICULTURE 



Issued November 1963 

Revised June 1965 

Washingtoa D.C. Slightly revised July 1976 

For sale by the Superintendent of Documents, U.S. Government Printing Office 
Washington, D.C. 20402 - Price $2.50 
25% discount allowed on order of 100 or more to one address 
Stock Number 001-000-03504-5 



ACKNOWLEDGMENTS 

The authors acknowledge the technical assistance of M. C. Audsley, H. G. 
Lento, A. J. Menna, T. S. Michener, J. Naghski, W. L. Porter, E. E. Stinson, and 
J. C. Underwood of the Eastern Regional Research Center, Agricultural Research 
Service; and F. E. Winch, Jr., Cornell University; the research work of J. W. Marvin 
and his associates at the University of Vermont; P. W. Robbins and R. N. Costilow 
and their students at the Michigan State University; and John Hacskaylo and 
James Callander, Ohio State Experiment Station; the cooperation of Lloyd M. 
Sipple, Bainbridge, N.Y., in developing and testing new equipment and procedures; 
and the facilities and equipment made available by the following maple sirup 
producers and equipment manufacturers; John Zimmerman, George Keim, Rey- 
nolds Sugar Bush, A. C. Lamb and Sons, Grimm Evaporator Company, Vermont 
Evaporator Company, George Soule Company, Gary Maple Sugar Company, and 
General Foods Corporation. The authors express their thanks for the assistance, 
support, and encouragement given in the preparation of this handbook by the 
National Maple Syrup Council, P. A Wells, C. F. Woodward, and Mrs. PhyUis K 
Davis. 



Trade names are used in this handbook solely to provide specific information. 
Mention of a trade name does not constitute a guarantee or warranty of the 
product by the U.S. Department of Agriculture or an endorsement by the 
Department over other products not mentioned 



CONTENTS 



Economics ^ 3 

Sugar maples 4 

The sugar grove 4 

Sap yields 6 

Summary 8 

Tapping the tree 8 

Date of tapping 9 

Selecting trees 9 

Boring tapholes 9 

Life of a taphole 11 

Sanitizing tapholes 12 

Summary 14 

Spouts and buckets 14 

Sap spouts 14 

Rainguards 16 

Sap buckets and bags 16 

Summary 18 

Collecting the sap 18 

Collecting tanks 19 

PipeHnes 20 

Summary 22 

Plastic tubing 23 

Installing tubing 24 

Taking down tubing 28 

Washing and sanitizing tubing 29 

Reinstalling tubing 33 

Summary 34 

Vacuum systems 35 

Storage tanks 35 

Summary 37 

Evaporator house on the sap-producing farm 37 

Location 37 

Function 38 

Requirements 38 

Design 38 

Steam ventilation 38 

Location of evaporator 41 

Air supply 42 

Sirup-processing room 42 

Fuel storage 42 

Summary 43 

The evaporator and its function 43 

Design of evaporator 44 

Changes in sap during its evaporation to sirup 44 

Evaporation time 45 

Liquid level in evaporator 46 

Rates of evaporation 47 

Rule of 86 48 

Summary 48 

Operating the evaporator , 49 

Starting the evaporator 49 

Drawing off the sirup 49 

Finishing pan 50 



Page 

Automatic drawoff 51 

End of an evaporation 52 

Cleaning the evaporator 53 

Summary 55 

Other types of evaporators 55 

Steam evaporator 55 

Vacuum evaporator 57 

Summary 57 

Fuel 58 

Wood 58 

Oil 58 

Summary 65 

Maple sirup 65 

Composition of sap and sirup 65 

Color and flavor 67 

Buddy sap and sirup 68 

Rules of sirupmaking 70 

Grades of sirup 70 

Summary 71 

Control of finished sirup 71 

Viscosity of maple sirup 71 

Effect of temperature on viscosity 72 

Old standards of finished sirup V2 

Use of precision instruments 72 

Elevation of boiling point 72 

Finishing pan 74 

Special thermometers 75 

Hydrometers 76 

Summary 78 

Clarification of sirup 78 

Sugar sand 78 

Sedimentation 79 

Filtration 79 

Summary 81 

Checking and adjusting density of sirup 82 

Weight method 82 

Refractometry method 82 

Hydrometry method 82 

Measuring density 85 

Measuring solids content 86 

Adjusting density 87 

Summary 88 

Grading sirup by color 89 

Color standards 89 

U.S. color comparator 89 

Summary 90 

Packaging 90 

Stack burn 91 

Control of micro-organisms 91 

Size and type of package 92 

Summary 92 

Standards for maple sirup for retail sale 93 

Summary 94 



m 



Maple products 94 

Equipment 95 

Maple sugar 96 

Maple cream or butter 98 

Fondant 100 

Soft sugar candies 100 

Maple spread 105 

Fluffed maple product 106 

High-flavored maple sirup 106 

Crystalline honey- maple spread 109 

Other maple products ^ 109 

Summary 110 

Testing maple sirup for invert sugar 113 

Simple test H"^ 

Quantitative test 114 

Determining invert sugar content of sirup 115 

Summary 115 



PaRC 

The central evaporator plant 116 

Location 117 

Size 117 

Design 117 

Operation 118 

Sap suppliers 120 

Purchase of sap 121 

Storing sap 122 

Handling and storing sirup 124 

Sanitation 125 

Economics 125 

Standardizing sirup for color and density 126 

Custom packaging and gift packages 126 

High-flavored and high-density sirup 127 

Manufacture of confections 127 

Summary 128 

References cited 128 

Supplemental reading 134 



MAPLE SIRUP PRODUCERS MANUAL 

By C. O. WILUTS" and CLAUDE H. HILLS, Eastern Regional Research Center, Northeastern Region, Agricultural Research 

Service 



No one knows who first discovered how to 
make sirup and sugar from the sap of the 
maple tree. Both were well-estabhshed items of 
barter among the Indians Hving in the area of 
the Great Lakes and the St. Lawrence River, 
even before the arrival of the white man {36, 
10 IV 

The maple crop, one of oui- oldest agricultural 
commodities, is one of the few crops that is 
solely American. Until only a few years ago, it 
was both produced and processed entirely on 
the farm. 

The last 20 years have witnessed some vast 
changes in the maple sirup industry. For the 
first half of this century, maple sap was col- 
lected and converted to sirup in much the same 
way as it was in 1900, when atmospheric evapo- 
ration equipment was developed by Yankee 
ingenuity (56). Many of the more recent 
changes have been the result of scientific and 
engineering studies carried out by the Eastern 
Regional Research Center in Philadelphia, Pa., 
and by the experiment stations and agricul- 
tural colleges of Michigan, New Hampshire, 
New York, Ohio, and Vermont. Recently the 
Forest Service has established a facility for 
research on maple sirup production at the 
Northeastern Forest Experiment Station in 
Burlington, Vt. 

Maple sirup is a woodland crop. Since the 
trees grow best at altitudes of 600 feet and 
higher, maple sirup is usually produced in hilly 
country. Its production is a vital part of the 
local economy in dozens of communities from 
Maine westward into Minnesota, and south to 
Indiana and West Virginia (chart 1). The same 
type and quality of maple products are pro- 
duced throughout the area. 




' Retired February 1969. 

- Italic numbers in parentheses refer to References 
Cited, p. 128. 



Chart l.^A and B , range of hard maple trees; A, range of 
commercial production of maple sirup. 

Maple sirup, like other crops, is subject to 
yearly fluctuations in production because of 
climatic and economic conditions. Production in 
the past has been affected by the cost or supply 
of white sugar and by the supply of farm labor. 
In 1860, a record crop of 4,132,000 gallons of 
maple sirup was produced. For the next decade 
the price of cane sugar declined. Production of 
maple sirup also declined to a low of 921,000 
gallons in 1869. As cane sugar became scarce 
during World War I, production of maple sirup 
again rose, slightly exceeding the 1860 record. 
Production also increased during World War II. 
Since then, production has decreased (table 1) 
(125, 126). 

The decreased production since World War II 
is a reflection of the shortage of farm labor 



2 AGRICULTURE HANDBOOK 134, U.S. DEFT. OF AGRICULTURE 

Table L — Maple sugar and sirup: Trees tapped, production, average price received by farmers, 
and imports. United States, selected years, 1918-70 ' 





Trees 
tapped 






Production 






Price ' 


Imports for 
consumption 


Year 


Sugar 
made 


Sirup 
made 

\ 


Total 
product in 
terms of 
sugar ■ , 


Average total 
product per tree 

As sugar ' As sirup - 


Per 

pound 

- of sugar 


Per 
gallon 
of sirup 


Sugar 


Sirup ' 


1918 


1,000 trees 
.. 17,053 
.- 14,070 
.- 13,158 

- 12,341 
._ 9,970 

- 7,685 
-- 8,090 
__ 6,138 


1,000 

pounds 

11,383 

3,238 

2,134 

1,241 

394 

202 

246 


1,000 

gallons 

4,141 

2,817 

3,712 

.3,432 

2,601 

1,030 

2,006 

■■^ 1,578 

^ 1,124 

1,266 

1,110 


1,000 
pounds 
44,511 
25,774 
31,830 
28,697 
21,202 

8,442 
16,302 
12,624 

8,992 
10,128 

8,880 


PouTids 
2.61 
1.83 
2.42 
2.33 
2.13 
1.10 
2.02 


Gallons 
0.33 
.23 
.30 
.29 
.27 
.14 
.25 
.26 


Cents 


Dollars 


1,000 
pounds 
. 3,807 
3,911 
9,735 
1,920 
4,087 
4,131 
6,549 
6,024 
5,742 
4,688 
3,561 


1,000 
pounds 


1925 

1930 

1935 

1940 

1945 

1950 

1955 


26.9 
30.2 
26.7 
29.4 
54.6 
77.2 


2.08 
2.03 
1.42 
1.65 
3.21 
4.12 
4.68 
4.96 
5.04 
6.83 


113 
1,575 
2,469 
4,660 
1,232 
5,282 
5,044 

10,009 
9,700 

10,549 


1960 








1965 








1970 

















' For 1918-40, production estimates for Maine, Maryland, Massachusetts, Michigan, New Hampshire, New York. Ohio, 
Pennsylvania, and Vermont; in 1945 Minnesota was added. 

- Assuming that 1 gallon of sirup is equivalent to 8 pounds of sugar. 

'Obtained by weighting State prices by quantity sold from 1945 to date; prior to 1945 weighted by production. 

I A gallon of sirup weighs about 11 pounds. 

' Includes sirup later made into sugar. 

SOURCES: Data for 1918-50 from Agricultural Statistics, 1957, table 133 {125). Data for 1955 and 1960 from Statistical 
Reporting Service and Economic Research Service, for 1965 and 1970 from Agricultural Statistics, 1972. table 137 (128). 



during this period. Although the trend in the 
country as a whole is downward, production of 
maple sirup in Michigan, Minnesota, and Wis- 
consin has increased. In fact, based on the 
number of tappable trees, production in these 
States could exceed production in New York 
and the Northeastern States. For example, 
Michigan has one-fifth of the total stand of 
maple trees. Canada's total maple crop is about 
double that of the United States. 

Table 2 shows the number of maple trees of 
tappable size and the percentage tapped in 
1951. 

Surveys in the eastern maple-producing 
areas (126) of the number of maple trees tapped 
as well as the total number of tappable size 
have shown that the industry is not suffering 
from too few trees. Although many sugar ma- 
ples have been cut for lumber, vast stands 
remain, and these stands can supply our maple 
sirup needs. 



Table 3 shows the production of maple sugar 
by the 11 principal States for selected years, 
1926-71. 



Table 2. — Tappable maple trees, and trees 
tapped. Eastern States, 1951 



State 



Tappable 
trees ' 



Trees tapped 



Thousands Number Percent 

Maine 53,553 136,000 0.25 

Maryland 1,660 28,000 1.7 

Massachusetts 11,913 166,000 1.4 

New Hampshire 12,103 261,000 2.2 

New York 73,128 1,960,000 2.7 

Pennsylvania 33,553 422,000 1.3 

Vermont 25,840 3,118,000 12.1 

West Virginia 13,031 

' Larger than 10 inches in diameter at breast height. 



MAPLE SIRUP PRODUCERS MANUAL 



Table 3.— Rank of States in production of maple sugar, selected years, 1926-71 



Rank 


1926 


1931 


1936 


1941 


1946 


1951 


1956 


1961 


1966 


1971 


1 


N.Y. 


Vt. 

N.Y. 

Ohio 

Pa. 

Mich. 

Wis. 

N.H. 

Mass. 

Md. 

Maine 


Vt. 

N.Y. 

Ohio 

Pa. 

Mich. 

Wi^. 

N.H. 

Mass. 

Md. 

Maine 


Vt. 

N.Y. 

Ohio 

Pa. 

Mich. 

Mass. 

N.H. 

Wis. 

Maine 

Md. 


Vt. 

N.Y. 

Ohio 

Mich. 

Pa. 

N.H. 

Mass. 

Wis. 

Maine 

Md. 


Vt. 

N.Y. 

Pa. 

Mich. 

Mass.. 

N.H. 

Wis. 

Maine 

Md. 

Ohio 

_Minn. 


Vt. 

N.Y. 

Ohio 

Pa. 

Wis. 

Mich. 

N.H. 

Mass. 

Md. 

Maine 

Minn. 


Vt. 

N.Y. 

Ohio 

Wis. 

Mich. 

Pa. 

N.H. 

Mass. 

Md. 

Maine 

Minn. 


N.Y. 

Vt. 

Wis. 

Pa. 

Mich. 

Ohio 

N.H. 

Mass. 

Md. 

Minn. 

Maine 


N.Y. 


2 


-. Vt. 


Vt. 


3 


- Ohio 


Ohio 


4 


Pa. 


Pa. 


5 


Mich. 


Mich. 


6 


N.H. 


Wis. 


7 


Mass. 


N.H. 


8 


_. Wis. 


Mass. 


9 


Maine 


Maine 


10 

11 


Md. 



















ECONOMICS 



Maple sirup, a noncultivated, nonfertilized 
crop derived from trees of the farm woodlot, 
provides supplemental cash incomes for many 
farmers, and it is the major cash crop for some 
farmers {2A, 26, 132, lUO, U2). The trees on 1 
acre will provide 160 tapholes and an average 
yield of 1 quart of sirup per taphole, or 40 
gallons of sirup per acre. At $10 per gallon, this 
sirup provides an annual per-acre gross income 
of $400. 

With the advent of the central evaporator 
plant, maple sap became a marketable commod- 
ity. Annual gross income for sap ranges from 
900 to $2.50 per taphole for sap delivered at the 
evaporator plant. 

The maple season is short and comes in the 
early spring when most other farm activities 
are slowest. Thus, it does not compete with 
other farm activities. Because the season oc- 
curs when off-farm employment is at a seasonal 
low, it fits well into a part-time farming pro- 
gram. 

Surveys in New York (5, 8), Ohio (63), Michi- 
gan {92), and Wisconsin (113) have shown that 
earnings from the production of maple sirup 
are among the highest on the farm. Wages 
average $3 per hour with a high of more than 
$5 for every hour spent in cleaning equipment, 
tapping trees, installing and taking down equip- 
ment, and collecting and boiling the sap. 

With the high annual cash crop and high 
wages earned in producing sap and sirup, it is 
difficult to understand why only 1 of 20 tappa- 
ble maple trees is being utilized. However, until 



recently maple sirup production methods were 
antiquated, at least when compared to modern 
methods of crop and livestock farming, and the 
unfavorable working conditions made sap col- 
lection and sirupmaking unattractive. 

Both equipment and processing methods are 
being modernized. Modernization should do 
much toward making maple sap and sirup pro- 
duction more attractive (71, U3). This moderni- 
zation includes plastic pipelines for collecting 
and transporting sap; taphole germicidal pel- 
lets; sanitary practices in tapping and sap han- 
dling; oil-fired evaporators; improved methods 
for evaporating sap, filtering sirup, and packag- 
ing the products; and the central evaporator 
plant. All these changes have reduced labor 
requirements and production costs, and have 
contributed to producing better grades of sirup 
that have a correspondingly greater value. Be- 
cause of the relatively high fixed costs for 
producing sirup on the farm, net income may be 
too low when sap from fewer than 500 tapholes 
is available, and the sap could be more profita- 
bly sold to a central plant. 

Sirup can be sold immediately to produce 
ready cash, or it can be held for a more favora- 
ble market or as a supply of raw material for 
producing more profitable maple products. If 
the sirup is held, it can be used as collateral for 
short-term loans. 

Since 1940, the proportion of the maple sirup 
produced in the United States that has been 
sold directly to the consumer by the producer 



AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE 



has increased. In many instances this has in- 
creased returns for the producer. To stabilize 
this expanded outlet, the producer has im- 
proved the appearance of the package and the 
quality of the sirup so that it meets State and 
Federal specifications. Many producers are ob- 
taining larger returns by converting their sirup 
to confections such as maple cream and hard 
and soft sugar candies. "^ 

Maple sirup producers" have formed associa- 
tions so they can pool their stocks. The chief 
functions of these associations are to maintain 
adequate supplies, to promote sales, and to 
maintain the quality of the products. A number 
of communities hold annual festivals to stimu- 
late interest in maple items. 

The central evaporator plant has made it 



possible for the first time to separate sap pro- 
duction from the processing of sap to sirup. 
Thus, farmers can realize a substantial income 
from maple sap without having to make large 
capital investments m an evaporator house, an 
evaporator, sap storage tanks, and miscella- 
neous equipment. 

The States, in cooperation with the Agricul- 
tural Research Service and the Extension Serv- 
ice of the U.S. Department of Agriculture, are 
conducting strong extension programs. These 
programs have brought the results of research 
directly to maple producers. In New York, a 
leader in this progranri, it is not uncommon for 
more than a thousand producers to attend the 
annual "maple sirup" schools held throughout 
the State in the premaple season. 



SUGAR MAPLES 



Only 2 of the 13 species of maple (Acer) native 
to the United States are important in sirup 
production (6, 55, 12i, 157). 

Acer saccharum Marsh, (better known as 
sugar maple, hard maple, rock maple, or sugar 
tree) furnishes three-fourths, of all sap used in 
the production of maple sirup. Although this 
tree grows throughout the maple-producing 
areas (chart 1), the largest numbers are in the 
Lake States and the Northeast. Trees grow 
singly and in groups in mixed stands of hard- 
woods. The trunk of a mature tree may be 30 to 
40 inches in diameter. The tree is a prolific 
seeder and endures shade well but unfortu- 
nately does not grow rapidly. It is best distin- 
guished by its leaf (chart 2). 

Acer nigrum Michx. F. (black sugar maple, 
hard maple, or sugar maple) grows over a 
smaller range than does A. sacchamm. It does 
not grow as far north or south but is more 
abundant in the western part of its range. This 
tree is similar to A. saccharum in both sap 
production and appearance. Its principal distin- 
guishing feature is the large drooping leaf of 
midsummer (chart 2). 

Other species of maples commonly found in 
our hardwood forests are the red maple Acer 
rubrum L.) and the silver maple (A. saccha- 
rinum L.). These trees, readily identified by 
their leaves (chart 2), are not good sources of 





RED MAPLE "' SILVER MAPLE 

Chart 2. — Leaves of the sugar maple (Acer saccharum 
Marsh.), red maple (A. rubrum L.), silver maple (A. 
saccharinum L.), and black maple (A. nigrum Michx. 

F.). 

maple sirup because their sap is less sweet than 
that of A. saccharum and A. nigrum, and it 
often contains excessive amounts of sugar sand. 
The red maple, the more common of the two, is 
easily identified in the spring by the red color of 
its buds. 

The Sugar Grove 

Most maple sugar groves, commonly called 
sugar bushes, are parts of stands of old hard- 



MAPLE SIRUP PRODUCERS MANUAL 



wood forests. In the ideal sugar grove, most of 
the other trees have been cut out and the 
maples have been thinned sufficiently to allow 
the trees to develop a good crown growth (,63). 
Thinning should be done according to a care- 
fully planned program, with the assistance of 
the State extension forester and the State for- 
ester for the area. If the stand is made up 
entirely of maples, approximately the same vol- 
ume of sap is produced per acre regardless of 
the size of the trees (^6). As the number of trees 
per acre decreases below 160 trees 10 inches in 
diameter at breast height (d.b.h.) or 40 trees 25 
inches d.b.h., the size of the crovvTis and the 
yield per tree may increase but the cost of 
collecting sap also increases because the dis- 
tance between trees requires longer sap mains 
when tubing is used, and sap collected by hand 
must be carried farther. 

Figures 1 and 2 show a maple grove with the 
large full crowns that are so important to the 
production of large amounts of sweet sap. 

For maximum returns, the grove should con- 
tain at least SOOtapholes, that is, a minimum of 
500 trees 10 inches d.b.h. Groves with fewer 



than 10 maple trees per acre are not profitable; 
groves with 30 to 40 trees 25 inches d.b.h. are 
ideal (<54). 

Maples grown in the open — for example, 
along the roadside (fig. 3) — are excellent sap 
producers (6Jf, 65, 67) not only because they 
have large crowns but also because they have a 
large leaf area, which is necessary for both 
starch and sugar production. Because of their 
shorter boles, roadside trees do not make as 
good saw logs as do trees that grow under 
crowded conditions. Studies have been con- 
ducted on the effect of fertilization {^6). 

Trees in a crowded stand have smaller 
crowns and therefore are not good sap produc- 
ers (figs. 4 and 5) because of their reduced leaf 
area. 

The ideal sugar grove (figs. 6 and 7) requires 
not only a planned spacing of trees but also a 
good understory to protect the ground, keep it 
moist, and permit growth of seedling maples to 
replace mature trees that should be cut down 
(fig. 8). Often these mature trees can be sold for 
lumber. However, there is no such thing as a 
dual-purpose maple tree — one that serves 




PN-469S 

Figure 1. — Grove of maple trees v/ith large crowns.which 
are needed for large yields of sweet sap. 



PN-4699 

Figure 2. — Same grove shown in figure 1 after defoliation, 
showing the branch structure of trees with large crowns. 



AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE 




PN-4700 

Figure 3. — Large-crowned maples, typical of roadside 
trees. 




PN-noi 
Figure U- — Trees in a crowded stand have small crowns 
and small boles. This ^rove requires thinning before it 
will be a profitable source of maple sap. 



equally well as a sap producer and as a source 
of lumber — because the factors favoring the 
growth of trees for the two purposes are not 
compatible. 

Consult your State extension forester, farm 
forester, and county agent and work with them 
to develop a management plan for your sugar 
grove. Aim for 160 tapholes per acre. 




PN-4881 

Figure 5. — Mixed stand of crowded trees. Some trees have 
long boles and small crowns. They make good saw logs 
but are poor sap producers. 




PN-no2 
Figure 6. — An ideal spacing of maple trees, favoring the 
growth of large crowns. 

Sap Yields 

The yield of sap in a sugar grove should be 
expressed in terms of the number of tapholes 
rather than the number of trees. The yield per 
hole is independent of the number of holes per 



MAPLE SIRUP PRODUCERS MANUAL 




PN-4703 

Figure 7. — This grove shows the effect of heavy grazing, a 
practice not recommended since it results in reduced 
sapwood production, stag-headedness, loss of reproduc- 
tion, and root damage caused by soil compaction. 




PN-170-1 

Figure 8. — Removing overmature trees that produce sap 
low in sugar content, to encourage growth of young 
stock. The high cut is made to avoid some of the sap 
stain and diseased wood associated with old tapholes. 

tree. A mean range per taphole is from 5 to 15 
gallons {95). However, a single taphole often 
produces from 40 to 80 gallons of sap in a single 
year — the equivalent of 3 or more quarts of 
sirup. 

The sugar content of the sap produced by 
different trees in a grove varies considerably 
(45, 110). The sap produced by the average tree 
has a sugar content of 2° to 3° Brix.^ Frequently 



' The density of sap and sirup is due to a mixture of 
dissolved solids and not just to sugar. The physical in- 
struments used to measure the density of sap and sirup 
do not distinguish between the density due to sugar and 
that due to other solids. The degrees Brix (° Brix) means 
that the solution has the same density as a solution 
containing a percentage of sugar numerically equal to the 
Brix value. 



trees produce sap with a sugar content of less 
than 1° Brix, and occasionally a tree produces 
sap with a sugar content of 9° or even 11° Brix. 
A conservative estimate is that the sap from 
four tapholes will yield 1 gallon of sirup. This 
sap most likely would have a density of 2.2^" 
Brix. Thus, 10 gallons of sap from each taphole 
would be required to yield 1 gallon of sirup. 

No device has been developed that will enable 
a maple sap producer to determine when sap 
will begin to run. However, sap will flow from 
the tapholes over a period of several weeks. The 
greatest yield of sap may be produced in a 
single run that occurs at the beginning of the 
period, at any time during the period, or at the 
end of the period. In 1960 almost all the sap 
crop was collected in a 24- to 48-hour period and 
the Brix value of the sap was much higher than 
2.2°. Many producers reported sap of 5° Brix 
and higher. Because of the large volume of sap 
collected in this short period, many producers 
reported that their buckets overflowed. How 
much was lost will never be known. This loss 
would not have occurred had plastic tubing 
been used for collecting and transporting the 
sap. 

Because of the large yield of sap in 1960 and 
its high sugar content, many producers who 
sold their sap to central evaporator plants re- 
ceived as much as $1.90 per taphole. A yield per 
taphole of 10 gallons of 5°-Brix sap having a 
value of 19.5 cents per gallon gives $1.95 per 
taphole. On this basis, a sugar grove with only 
100 tapholes per acre would produce a gross of 
$195 per acre. This may answer the question 
that has often been raised as to whether the 
sugar orchard should be operated to produce 
sap or should be cut and sold as lumber. 

The yield and sweetness of the sap produced 
by a tree vary from year to year, but trees that 
produce sap with a high sugar content and 
trees that produce sap with a low sugar content 
maintain their relative positions from year to 
year {112). It is important to know the exact 
sugar content of the sap produced by each tree. 
Measuring the sugar content of sap is not 
difficult. All that is needed is a sap hydrometer 
or refractometer and a thermometer. 

To make the reading, float the hydrometer in 
the sap bucket or in a hydrometer can contain- 
ing the sap (fig. 9). Also, obtain the temperature 



AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE 




PN-4706 

Figure 9. — Measuring the density of sap C Brix) with a 
precision hydrometer cahbrated in 0.1°. If the bucket 
contains too little sap to provide the necessary depth 
for the measurement, transfer the sap to a hydrometer 
can. 

of the sap so the hydrometer reading can be 
corrected. (The sap should contain no ice.) Sub- 
tract 0.4° Brix for temperatures of 32f to 50° F., 
0.3° Brix for temperatures of 51° to 59°, and 0.1° 
Brix for temperatures of 60^ to 68". 

The sap hydrometer is usually calibrated 
from 0° to 10° Brix, with divisions of 0.5°. A 
more accurate measurement can be obtained 
by using a hydrometer with divisions of 0.1° (fig. 
9). 

The amount of sugar in sap is of great eco- 
nomic importance. A taphole that produces 15 
gallons of sap with a sugar content of 2° Brix 
yields 2.5 pounds of sugar, or one-third gallon of 
sirup; whereas a taphole that produces 15 gal- 
lons of sap with a sugar content of only 1° Brix 
yields only 1.3 pounds of sugar, or less than one- 



fifth gallon of sirup. The cost of producing the 
sirup from both tapholes is approximately the 
same. Trees producing sap with a sugar content 
of 10° Brix are especially profitable, as 15 gal- 
lons of sap from 1 taphole yields nearly P/4 
gallons of sirup, or more than five times as 
much as the 2°-Brix sap. Trees that produce sap 
low in sugar (1° Brix or less) should be culled. 

Research is being conducted at the Universi- 
ties of Vermont and New Hampshire, at the 
Ohio Agricultural Experiment Station, and by 
the U.S. Forest Service on the propagation of 
maple trees from selected high-yielding trees 
(20, 32, 33, 3U, U5). This research should eventu- 
ally make it possible to set out maple orchards 
or roadside trees that will produce sap with a 
high sugar content. 

Use of a germicidal pellet to prevent prema- 
ture drying up of a taphole may increase sap 
yields as much as 50 percent. Since the results 
obtained by using the pellet are due to its 
germicidal action, it will not increase the sap 
crop in sugar groves where sanitary measures 
are already being practiced. 

Summary' 

(1) Consult your State extension forester, farm 
forester, and county agricultural agent and 
work with them to develop a management 
plan for your sugar grove. Aim for 160 
tapholes per acre (160 trees 10 inches d.b.h. 
or 40 trees 25 inches d.b.h.). 

(2) Remove all defective, diseased, and weed 
trees. 

(3) Check the yield and sugar content (° Brix) of 
the sap from each tree. Cull trees that yield 
sap low in sugar (1° Brix). 

(4) For maximum sap yields use germicidal 
taphole pellets. 



TAPPING THE TREE 



The sap of the sugar maple, from which sirup 
and sugar are made, differs in composition from 
the circulatory sap of a growing tree. We know 
little concerning this sap, or sweet water as it is 
called in western Pennsylvania. Intensive 
study of maple sap at the University of Ver- 
mont (3U, 35, 57-59) should lead to a better 



understanding of its nature, function, and 
source, and of the factors responsible for sap 
flows. 

Sap will flow any time from late fall after the 
trees have lost their leaves until well into the 
spring, each time a period of below-freezing 
weather is followed by a period of warm 



MAPLE SIRUP PRODUCERS MANUAL 



weather. The sap will flow from a wound in the 
sapwood, whether the wound is from a cut, a 
hole bored in the tree, or a broken twig. 

Date of Tapping 

To establish a rule of thumb that can be used 
to set the date for tapping sugar maples is not a 
simple matter. The date should be early enough 
to assure collecting large early flows of sap (66). 
Michigan and New York provide sugarmakers 
with radio weather forecasts of the correct 
tapping dates (22). A similar service is being set 
up in other maple-producing States including 
Massachusetts, Vermont, and Wisconsin. Gen- 
erally, trees should not be tapped according to a 
calendar date. In 1953 when this practice was 
followed, many producers failed to collect the 
large early flow that resulted from an unsea- 
sonable, early warm spell. The danger of tap- 
ping too early is now largely eliminated 
through use of germicidal taphole pellets (17). 
When pellets are used, trees can be tapped 
several weeks ahead of the normal season. 

Selecting; Trees 

Selecting trees for tapping is of greatest im- 
portance and can be done at any time through- 
out the year. 

Trees that produce sap with a density of only 
1° Brix, as determined with a sap hydrometer 
or refractometer, should be culled. Culling must 
be done during the period of sap flow (64). If 
time does not permit testing all the trees dur- 
ing one sap season, test as many as possible the 
first year and test the remaining trees during 
succeeding years. 

Trees selected for tapping should have a 
minimum diameter of 10 inches at 4V2 feet from 
the ground (d.b.h.) (fig. 10). 

A good rule (H, 6i) for determining the num- 
ber of tapholes that can safely be made in a 
single tree is as follows: 

Tapholes 

Diameter of tree, per tree,' 

inches number 

Less than 10 

10 to 14 1 

15 to 19 2 

20 to 24 3 

25 or more 4 

' Number of buckets. 




PN-4706 

Figure 10. — Measuring the diameter of the tree to deter- 
mine the number of tapholes the tree will support. 



To undertap a tree reduces the potential size 
of the crop without any benefit to the tree. On 
the other hand, to overtap (fig. 11) may seri- 
ously damage the tree (72, 94). 

Once the trees have been measured, they 
should be marked so they will not have to be 
remeasured each season. This can be done by 
painting a numeral or a series of dots on the 
tree or by using paints of different colors, such 
as white for 1 taphole, yellow for 2 tapholes, etc. 

Boring Tapholes 

Tapholes are made by boring with either a ^/e- 
inch or a ''/le-inch fast-cutting wood bit. Al- 
though tapholes can be bored by hand with a 
carpenter's brace (fig. 12), this method is used 
only for very small operations. 

For large operations, a portable motor-driven 
drill not only speeds up the operation but also is 
far less fatiguing. These drills are made in two 
basic designs, one powered by a gasoline motor 
and the other by an electric motor. In one of 
the earlier models that is still popular (fig. 13), 
the gasoline motor is mounted on a packboard 



10 



AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE 




PN^707 

Figiire 11. — Overlapped tree (8 buckets on a 4-bucket 
tree). Note attempt to tap over large roots. 




PN-170K 

Figure 12. — Boring the taphole at convenient breast 
height. The hole is 6 inches from that bored the pre- 
vious season. 



and is connected to the drill by a flexible shaft. 
In other models, the drill is attached directly to 
the gasoline motor, which is held in the hand. 

The electric battery-powered drill (figs. 14 
and 15) is newer than the gasoline-powered 
drill. It is light and free from vibration and is 
fast becoming popular. With either a gasoline- 
or an electric-powered drill, one man can drill 
holes as rapidly as a crew of two or three can 
set the spouts and hang the buckets or bags, or 
install the tubing. 

The hole is bored into the tree, preferably at 
a downward pitch of approximately 5 degrees. 
The downward pitch is especially desirable if 
germicidal pellets are used in the tapholes. The 
hole is bored 3 inches deep or until stained 
heartwood is reached. Studies at Michigan 
State University {57) have shown that a taphole 
3 inches deep (fig. 16) produces up to 25 percent 
more sap than a taphole only 2 inches deep. 

The position of the first taphole is selected 
arbitrarily. The hole should be 2 or 3 feet above 
the ground or, if there is snow on the ground, 
as close as possible to this height. This low 
position is particularly well suited to the use of 
plastic tubing. The compass location of the hole 
is not important. Data obtained in New York 
(m) and in Michigan {16, 93, H, 96) have shovm 
that the total yield is essentially the same 
regardless of the compass location of the hole. 
However, the warm side of the tree is favored. 
Data also show that the height above ground 
level has little effect on yield. The best practice 
is to make the new taphole on successive years 
6 to 8 inches from the previous year's taphole, 
working up the tree in a spiral pattern (fig. 17). 
With this procedure, the producer may tap his 
tree year after year in different quadrants and 
avoid striking an old taphole or dead tissue that 
has been hidden by new bark, either of which 
would result in a smaller flow and poorer qual- 
ity sap. 

When plastic tubing is used to collect sap, 
there is no minimal distance at which the 
taphole is located above the ground, and an 
even larger area of the tree becomes available 
for tapping. This permits a longer interval be- 
tween periods when a repeat tap has to be 
made in the same area of the tree. 



MAPLE SIRUP PRODUCERS MANUAL 



11 




PN-n09 

Figure 13. — A gasoline-powered portable tapping drill 
with flexible shaft. 




PN-4711 

The power tapping drill permits drilling the 
hole at different heights. 




rN-niii 
Figure H. — An electric battery-powered tapping drill. 



The time required for new bark to grow over 
a taphole depends on the health and vigor of 
the tree. It is not uncommon to find the hole 
nearly covered in a year (fig. 18). The hole itself 
remains open, but fungus growth (109) may 
occur in the new hole and stain the wood 
several inches above and below the hole and an 
inch or less to the side (figs. 19 and 20). 



Figure 16. — The taphole is bored into the tree 3 inches 
deep. 

Life of a Taphole 

A taphole should be usable from the time it is 
bored until the buds begin to swell and the 
sirup acquires an unpalatable or buddy flavor. 
In the past, the taphole often dried up within 3 
or 4 weeks after the hole was bored. Drying up 
is caused by growth of micro-organisms in the 



12 



AGRICULTURE HANDBOOK 134, U.S. DEFT. OF AGRICULTURE 



taphole rather than by air drying of the wood 
tissue (13, 102, 103). When the microbial growth 
has reached a count of 1 million per cubic 
centimeter, sap will no longer flow from the 
hole, and it is said to be dried up (J7). 

In the past, a dried-up taphole was reamed to 
make it flow again; it was assumed that this 
procedure would remove the air-dried wood tis- 
sue. However, reaming was never successful. 
Research has shown that the reaming bit did 
not sterilize the hole. Reaming removed only a 
layer of the microbial deposit; the remaining 
bacteria kept on growing. Soon, sufficient num- 
bers were again produced to stop the flow of 
sap. The newly developed germicidal pellets 
have prevented premature drying of the tap- 
hole. 





PN-4714 

Figure 18. — In a healthy, vigorously growing tree, the 
taphole will be completely covered with new wood and 
bark in 1 year. 




Figure 17: 



PN^ni:) 
-Tapholes arranged in a spiral about the tree. 



Figure 19. — A split section of a tapped maple log showing 
the longitudinal stain area above and below the tap- 
hole and the new growth of bark that has covered the 
outside end of the hole (left). 

Sanitizing Tapholes 

Germicidal Pellets 

A germicidal taphole pellet (fig. 21) has been 
developed at Michigan State University (17). If 
put into the taphole as soon as it is bored, the 



MAPLE SIRUP PRODUCERS MANUAL 



13 




PN-4716 

Figure 20. — Cross section of a maple log showing stained 
area caused by fungus growth in old tapholes. The 
stains show the exact contour of the holes including the 
area entered by the screw of the bit, but do not indicate 
whether the holes lie above or below the plane of the 
cut. Note that the stain is confined to the width of the 
taphole, which indicates that the lateral damage to the 
tree is restricted to within one-half inch on each side of 
the hole. But damage may extend several inches above 
and below the hole, as shown in figure 19. 

pellet will keep the hole essentially sterile 
throughout the sap season (6 to 10 weeks) and 
therefore will permit flow of sap H, 5, 6) each 
time the weather is favorable. If large early 
flows of sap occur, a second pellet may be 
needed after 4 weeks. The active ingredient of 
the pellet is paraformaldehyde which, because 
of its germicidal effect and low solubility, makes 
it ideally suited to this use. Each pellet must 
contain a minimum of 200 milligrams of availa- 
ble formaldehyde at the time it is placed in the 
taphole. 

The function of the pellet is to contribute 
enough formaldehyde to the 1 to 5 milliliters of 
sap remaining in the taphole between flow 
periods to keep microbial growth to a minimum. 
When the sap is flowing, the short time it is in 
contact with the pellet permits only a trace of 
formaldehyde (less than 5 p.p.m.) to be dis- 
solved. This small amount of formaldehyde is 
removed from the boiling sap while it is being 
concentrated to sirup in the evaporator pan. 



The very low concentration of formaldehyde in 
the sap in the storage tanks will not maintain 
the sap in a sterile condition {133, 13 Jf). This is 
fortunate because it is sometimes desirable to 
culture the sap with specific micro-organisms or 
enzymes. Sap is cultured as one step in produc- 
ing high- flavored maple sirup; it is also cultured 
to destroy substances that are responsible for 
the buddy flavor in "buddy" sap («). Other 
germicides are under investigation (W, AD- 

Because of the very low residue of formalde- 
hyde in sirup, the U.S. Food and Drug Adminis- 
tration issued in February 1962 a regulation 
governing its use {130). 

However, under no circumstances should 
more than one paraformaldehyde pellet be 
placed in a taphole, nor should formaldehyde be 
added to the storage tanks. To do either might 
raise the concentration of formaldehyde in sap 
and contribute to a high concentration in the 
sirup. This would produce sirup containing 
more formaldehyde than specified in regula- 
tions of the U.S. Food and Drug Administration 
or of the State in which the sirup is made. 




PN-4717 

Figure 21. — A germicidal pellet is inserted in a taphole 
immediately after the taphole has been drilled or after 
it has been flushed with hypochlorite solution. 



14 



AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE 



While pellets were being developed and dur- 
ing the first 2 years they were used commer- 
cially (1962-63), records show that when 
weather was favorable to microbial growth in 
the tapholes, pellets doubled or trebled the yield 
of sap. Pellets are less effective when good 
sanitary practices are followed or when the 
entire maple season remains cool, since micro- 
bial growth is retarded under these conditions. 

Elimination of the cause of premature drying 
of the taphole permits tapping the tree before 
the sap season with the assurance that the first 
as well as the late run of sap will be obtained. 
Also, the cause of diminished flows throughout 
the season is eliminated. Both of these factors 
increase yields of high-quality sap and decrease 
the man-hours required to harvest sap (156). 
Germicidal pellets are especially desirable 
where plastic tubing is used to collect and 
transport sap in the woods. The pellets help to 
keep the pipeline (tubing) clean and sterile. 

Chlorinated Solutions 

In many sugar groves, chlorinated solutions 
are being used to control microbial growth in 
the taphole {133). The best procedure is to flush 
the taphole as soon as it is drilled with a 
solution consisting of 10 parts of a commercial 
hypochlorite solution (containing approxi- 
mately 5.25 percent of sodium hypochlorite) and 
90 parts of water (fig. 22). 

Often where there is a week or more between 
sap runs and particularly if the nonrunning 
period is warm, the tapholes should be re- 
flushed with a solution of the same strength. 
Where this chlorination procedure has been 
practiced, a change to germicidal pellets may 
not increase sap yields. 

Summary' 

(1) Do not tap by the calendar. Follow your 
State's maple weather reports. 

(2) Tap before the sap-flow season. 




PN-4718 

Figure 22. — Flushing the taphole with a 10-percent 
commercial hypochlorite solution. 

(3) Make 1 taphole in a tree 10 inches in diame- 
ter and 1 additional hole for each additional 
5 inches of the tree's diameter. 

(4) Make the taphole with a ^'/s-inch or '/le-inch 
fast-cutting (special) wood bit. 

(5) Use a power tapper if the grove is large 
enough to justify the expense. 

(6) Bore the hole into the tree to a depth of 3 
inches at a slight dov^Tiward pitch. 

(7) The location of the taphole in respect to 
compass position and roots is not important. 

(8) Space the holes at least 6 inches apart 
(circumference of tree) and in a spiral pat- 
tern. 

(9) Sanitize the taphole. Use 1 germicidal pellet 
per taphole. 



SPOUTS AND BUCKETS 



Sap Spouts 



The spout or spile has three important func- 
tions: (1) It conveys the sap from the taphole to 
a container; (2) it either connects the plastic 



tubing to the taphole or serves as a support on 
which to hang the sap bucket or bag; and (3) it 
keeps adventitious (wild or stray) bacteria from 
gaining access to the moist taphole, which 
should reduce infection if plastic tubing is used. 



MAPLE SIRUP PRODUCERS MANUAL 



15 



Over the years a large number of sap spouts 
have been designed and used, with special fea- 
tures claimed for each. The earliest spouts were 
hollow reeds, often a foot or more in length. 
Two reeds inserted in adjacent tapholes carried 
the sap to the same container (fig. 23). There 
are only a few basic differences in the design of 
the various sap spouts. Some have a large 
opening at the delivery end. Others have a hook 
to support the bucket and a hole for attaching 
the bucket cover. On others the bucket is sup- 
ported directly on the spout. All commercial 
spouts are satisfactory. A few spouts are shown 
in figure 24. 

Plastic spouts are used with plastic tubing 
and they have tubulations to which the tubing 
is attached. 

All spouts have a tapered shoulder so that 
when they are driven into position in the tap- 





PN-ni9 
Figure 23.— Reed sap spouts, the forerunner of metal 
spouts. 



Figure 2U- — Wood and metal sap spouts. 

hole, they form a watertight seal with the bark 
and outer sapwood but leave a free space be- 
tween the sapwood and the spout. In setting 
the spout (fig. 25), care must be exercised not to 
split the tree at the top and bottom of the 
taphole. A split results in sap leakage and often 
all the sap from that hole is lost. To strike the 
bark a sharp blow damages the tree and often 
kills an area for several inches. 

Spouts should be cleaned at the end of each 
season. Metal spouts can be washed by tum- 
bling in a small concrete mixer containing a 
solution of a good detergent. Just before the 
spouts are taken into the sugar grove at the 
beginning of a sap season, they must be steri- 
lized by heating them in boiling water for 15 
minutes or longer. The spouts are then put in a 
pail and covered with a chlorine solution con- 
taining 1 cup of a commercial bleach (5.25 per- 
cent of sodium hypochlorite) in 1 gallon of 
water. The pail of chlorine-wetted spouts is 
carried into the sugar grove. Rubber or rubber- 



16 



AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE 




Figure 25. — Setting the sap spout. 



coated canvas gloves must be worn to protect 
the hands from the strong bleach. 

Rain^uaixls 

Heavy rains often occur during the sap sea- 
son. Rainwater running down the tree picks up 
dirt and leaches tannins from the bark. Both 
the dirt and the tannins, if permitted to get into 
the sap bucket, lower the grade of the sirup 
produced. Most sap spouts are provided with 
"drip tips" to deflect runoff rainwater from the 
tree and prevent it from entering the bucket. In 
heavy downpours, drip tips are often inade- 
quate. Use of a simple, homemade rubber rain- 
guard (fig. 26) prevents the heaviest runoff 
rainwater from entering either a sap bucket or 
bag. 

To make a rainguard, cut a 2-inch square 
from a thin sheet of rubber, such as an old 
inner tube. With a leather punch, cut a ^/le-inch 
hole in the center of the square. Slip the rain- 




PN-4722 

Figure 26. — Rubber rainguard prevents water from 
reaching the sap bucket. 



guard over the end of the spout near the tree 
and set it far enough forward so that when the 
spout is seated in the taphole there will be a 
free space of V4 to ^/s inch between the rubber 
guard and the bark of the tree. 

Sap Buckets and Bags 

Three types of containers have been used to 
collect the sap from the spout: (1) The wooden 
bucket; (2) the metal bucket; and (3) the plastic 
bag. 

The wooden bucket, because of its size and 
the care required to keep it watertight, has 
largely disappeared from use. 

Zinc-coated 15-quart buckets are the most 
commonly used metal buckets. Large 20-gallon 
galvanized cans that eliminate daily collection 
of sap are used in some "cold" sugar groves 
(high altitude, northern exposure). In a cold 
grove, the buckets often contain ice sap which 
retards microbial growth. The minute amount 
of zinc that is dissolved from the galvanized 
coating by the sap tends to reduce microbial 
growth, but the germicidal effect is nullified- if 
the zinc coating is overlayed with a deposit 



MAPLE SIRUP PRODUCERS MANUAL 



17 



from the sap (108). It can be made effective 
again by carefully removing the protective film 
overlaying the galvanized surface. The 20-gal- 
lon containers tend to reduce microbial growth 
more than do the smaller buckets (28). Lead- 
coated metal (terneplate) or lead-soldered buck- 
ets and buckets painted with lead paint should 
not be used because the lead may be dissolved 
by the sap, especially sap that has been allowed 
to ferment and sour. Sirup made from this sap 
may contain illegal amounts of lead. Aluminum 
buckets, which are being subsidized in Canada, 
tend to eliminate most objections to metal 
buckets. 

Every bucket should be provided with a cover 
to keep out rain and falling debris. Covers are 
of two general types: Those that are attached 
to the spout (fig. 27) and those that are clamped 
to the bucket (fig. 28). 

The plastic sap bag (fig. 29), a comparatively 
recent development, met with much favor, espe- 
cially before the development of plastic tubing. 



Some advantages of plastic bags are: (1) Be- 
cause of their small bulk and weight, they 
require minimum storage space, and they are 
easily transported to the woods and hung. (2) 
They have a self-cover that encloses the spout 
when the bag is in place, and thus limits access 
of micro-organisms to the open end of the spout 
and to the taphole. (.3) Emptying the sap is a 
one-handed operation (fig. 30). The bags need 
not be removed from the spout; they can be 
rotated on the spout. (4) Because they are 
transparent to sunlight radiation, which is le- 
thal to micro-organisms, they tend to keep the 
sap sterile (76). Sterile sap contributes to the 
production of high-quality sirup. 

Some disadvantages of plastic bags are: (1) 
They may open at seams, especially if the sap 
in a filled bag freezes. (2) They are difficult to 
empty when filled with ice. (3) The bag may be 
too small to hold a day's run. (4) The bags are 
subject to damage by rodents. (5) Washing and 
rinsing the bags may be difficult. 




PN-4723 

Figure 27. — Sap bucket cover attached to the spout by 
means of a pin. With this type of cover, the bucket must 
be lifted free of the spout for emptying. 



PN-1724 

Figure 28. — A clamp-on cover stays fixed to the bucket 
and is not easily blown off. With this type of cover, a 
bucket that is attached to the spout by means of a hook 
must be lifted free of the hook for emptying. However, 
a bucket that hangs on the spout by means of a large 
hole that will slip over the spout can be emptied by 
rotating the bucket and cover on the spout. 



18 



AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE 




PN-4725 

Figure 29. — Plastic sap bag: The amount of sap is easily 
seen and accumulations of sap, even from short runs 
over a long period of time, tend to remain sterile 
because ultraviolet rays of daylight are transmitted 
through the plastic. The bag has its own plastic cover. 
Since the spout is completely covered, it is free from 
contamination. 



Summary 

(1) Any commercially available spout is satis- 
factory. 

(2) Use only clean, sterile spouts. 

(3) Drive the spout into the taphole with a firm 
enough blow to seat it securely, but do not 
drive it so far as to split the bark and wood. 



PN-4726 

Figure SO. — Emptying the plastic bag by rotating it on 
the sap spout makes it a one-handed operation. 



(4) Use a 2- X 2-inch rubber runoff rainguard on 
the spout. 

(5) Carry clean, sterile spouts wetted with a 
dilute, hypochlorite solution into the sugar 
grove. 

(6) Do not use buckets coated with lead paint or 
with temeplate. 

(7) Use containers large enough to hold a nor- 
mal day's run of sap. 

(8) Use only clean sap buckets or bags. 

(9) Use covers on all sap buckets or bags. 



COLLECTING THE SAP 



Collecting (gathering) sap by hand (fig. 31) is 
the most expensive and laborious of all maple 
sirupmaking operations and accounts for one- 
third or more of the cost of sirup production. 

When buckets or sap bags are used, much 
time can be saved if the trees to be serviced on 
both sides of a roadway bear a mark to distin- 
guish them from the trees to be serviced from 
an adjacent roadway. This prevents servicing 
the same tree from both roadways. Different 
colored paints can be used to mark the trees. 



Another timesaver requires punching a sec- 
ond hole in the sap bucket opposite the original 
hole, and painting a stripe from that hole to the 
bottom of the bucket. The buckets are hung 
first from one hole (for example, with the stripe 
away from the tree and plainly visible); after 
they are emptied, they are hung from the 
opposite hole. This makes it easy for the sap 
collector to tell whether a bucket has been 
emptied and keeps him from skipping full buck- 
ets as well as wasting time revisiting empty 



MAPLE SIRUP PRODUCERS MANUAL 



19 




Figure 31. — Collecting sap by hand is expensive. Usually 
two pails are used to collect the sap from the sap bags 
or buckets, and the sap is carried by hand to the 
collecting tanks. 



buckets. The only objection is that a bucket 
with holes on both sides holds less sap than a 
bucket with one hole because it hangs from the 
spout at an angle. 

Some producers empty the buckets by rotat- 
ing (spinning) them on the spout. This requires 
the use of a cover attached directly to the 
bucket and a spout on which the bucket is hung 
by means of a hole in the bucket. More sap may 
be spilled when buckets are emptied by spin- 
ning than when they are lifted free of the spout 
and tree. Spillage of sap when transferring it 
from bucket to gathering pail and from pail to 
collecting tank may account for an appreciable 
loss of the sap crop. Plastic tubing eliminates 
this loss (fig. 32). 

Sap must not remain in the buckets more 
than a few hours before it is collected. During 
short runs that produce too little sap to war- 
rant collecting, the buckets must be emptied, 
even though this is time consuming and expen- 
sive. The sap left standing in the bucket will 
ferment and spoil and will spoil other sap to 
which it is added in the collecting or storage 
tanks. 




PN^728 



PN^7 

Figure 32. — No labor is required when tubing is used to 
collect sap. 



Collecting Tanks 

Collecting tanks vary in size according to the 
needs of the sugar grove. The tanks usually are 
provided with a strainer, baffled to prevent loss 
of sap by splashing, and a drainpipe. 

The method of hauling the tank is governed 
by conditions in the sugar grove. The tank can 
be mounted on any of several types of carrier, 
including stoneboat or skids, 2-wheel trailer, 
high wheeled wagon gear, and underslung rub- 
ber-tired, 2-wheel trailer (fig. 33). 

High-mounted tanks should be avoided be- 
cause of the labor required to lift the sap (fig. 
34). Usually an additional worker is needed. 

A rig of excellent design has a low-mounted 
sump tank and a self-contained, power-driven 
pump to lift the sap up to the large tank (figs. 
35-38). 

A new type of collecting tank being widely 
adopted employs vacuum (suction) for filling. 
Tanks to be filled by suction must be airtight 
and structurally strong enough to withstand an 
external pressure of 15 pounds per square inch 
(1 atmosphere). Tanks larger than 300 gallons 
require internal bracing. The vacuum can be 
obtained by a separate pump or by connecting a 
line from the manifold of the truck or tractor 
engine (fig. 39). To prevent sap from entering 
the engine manifold, a float check valve is 
mounted on the tank and the vacuum line is 
attached to this (fig. 40). The check valve is 



20 



AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE 



/ \ w^hB^^y^^HHE^^^HuA^lBflS 



PN-4729 

Figure SS. — Collecting tank mounted on a truck body. 
This type of assembly does not require special rigs, but 
an additional man is needed to empty the pails into the 
tank. 




PN-n3n 
Figure Si. — Additional labor is required to lift sap to a 
tank mounted on a trailer. 



similar to those used in milking machines that 
prevent milk from entering the pump. If sap 
reaches the motor, it causes serious damage. 

A 1,000-gallon tank can be emptied and put 
back into operation in only a few minutes. The 
suction line is a 1-inch hose, which will pick up 
30 gallons of sap per minute. Instead of a slow- 
acting valve in the suction line, a tapered plug 
is used in the pickup end of the hose. This plug 
is removed just before the hose is submerged in 
the sap in the tank or bucket to be emptied. 




PN-4731 

Figure S5. — For large operations or for collection from 
roadside trees extending along several miles of roads, 
the large tank trailer is desirable. 

If a closed tank and an engine manifold 
vacuum system is not available, a pump-and- 
vacuum system can be used (2). In this novel 
system, an air-cooled gasoline motor operates a 
pump which, in turn, creates a vacuum in a 
small tank. The sap is discharged into a conven- 
tional collecting tank. 

Regardless of how the vacuum in the suction 
(sap pickup) line is developed, this method of 
collecting sap is efficient and fast, causes a 
minimum of loss due to spillage, and can be 
used for collecting sap from the conventional 
metal bucket, from the large 20-gaIlon con- 
tainer, and from small and large storage tanks. 
Whether or not the collecting tank has a vac- 
uum line pickup, the tank must be as large as 
roads and other conditions will permit. The 
smaller the tank, the greater the number of 
costly trips that must be made. 

Pipelines 

Metal pipelines have been used in the maple 
sugar grove for 50 years or more. The early 
metal pipe carried the sap over almost impassa- 
ble terrain, from one sugar grove to another or 
to the evaporator house (figs. 41 and 42). Metal 
or wooden troughs have also been used as 
"pipelines." 

All these pipelines, whether metal pipe or 
metal or wooden troughs, had one serious draw- 



MAPLE SIRUP PRODUCERS MANUAL 




Figure 36. — Sap is easily poured from buckets into a low 
sump tank, from which it is pumped into the large tank. 



PN^733 

Figure 37. — The sap is lifted from the sump by means of a 
pump. Power for the pump can be supplied by a takeoff 
from the tractor or truck engine or by a small gasoline 




PN-4734 

Figure 38. — Vacuum lines operated by a vacuum pump 
can be used to empty buckets and small containers in 
the woods or at the roadside. 



PN-4735 

Figure 39. — The vacuum is obtained from the manifold of 
the truck engine. 



22 



AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE 




Figure 40. — Float valve assembly and vacuum (suction) 
line. 

back; they had to be installed with great care so 
that there would be no sags in the line. Sags in 
pipes permitted the sap to lie there and, when a 
freeze occurred, the ice formed would often 
burst the pipe. Sags in troughs permitted the 
sap to overflow. In addition, metal pipe was 
hard to clean. Since metal pipes are opaque, 
there is no simple means to determine when 
they are clean. Nevertheless, the saving in time 
and labor made possible by these earlier pipe- 
line systems justified their use. 

Suimnai*y 

(1) Collecting sap by hand and hauling it is the 
most expensive operation of sirupmaking. 
Examine all steps and introduce laborsav- 
ing methods where possible. 




PN^737 

Figure il. — Use of pipelines to carry sap over impassable 
areas saves time. With a lateral system of dumping 
stations, collecting tanks can be eliminated in some 
locations. The pipeline also makes accessible some 
sugar groves that would be impossible to reach by 
tractor or truck. 




PN^738 
Figure 42.— When the sugar grove is at a higher elevation 
than the evaporator house, the pipeline carries sap 
from dumping stations at the edge of the sugar grove 
to the evaporator house. This eliminates long and 
costly hauls of sap. 

(2) Wherever possible, use pipelines to trans- 
port the sap. 

Do not collect spoiled sap. Do not allow 
small runs of sap to remain in the buckets. 
Do not spill sap when pouring it into collect- 
ing pails and tanks. This can account for a 
10-percent loss. 

(5) Use as large a collecting tank as possible to 
avoid repeated hauls. 

(6) Use a -pump or vacuum to fill the tank. 

(7) When vacuum is used, be sure the tank is 
internally braced to withstand the high ex- 
ternal pressures. 

(8) Keep all equipment sanitary at all times. 



(3) 



(4) 



MAPLE SIRUP PRODUCERS MANUAL 

PLASTIC TUBING 



23 



With the advent of plastic tubing, most of the 
objections associated with metal pipes have 
been overcome. Not only can plastic tubing be 
used for collecting and transporting the sap, 
but also it is cheaper to install, it has greater 
flexibility and elasticity, and it is easy to keep 
clean. Wide acceptance of plastic tubing by 
maple producers (.38) has been a major factor in 
modernizing the 300-year-old maple industry. 

Use of plastic tubing has practically elimi- 
nated the hard, unattractive labor of collecting 
sap and has lowered the cost of sirupmaking as 
much as 40 percent. No longer is it necessaiy to 
construct expensive roadways through the 
woods to support heavy tanks of sap and to 
open these roads after heavy snows (fig. 43). 
Tapping need not be delayed until the sap 
season has arrived. Large crews do not have to 
be hurriedly assembled to tap the trees and 
hang the buckets. Instead, the lightweight plas- 
tic tubing can be carried by hand through the 
woods when convenient. 

Some setbacks were encountered when plas- 
tic tubing was first introduced. Since it had 
been emphasized that sap issues from the tree 
under high pressure (,39), systems for installing 
the pipelines were patterned after those used 
for high-pressure waterlines. It was anticipated 
that enough pressure was developed by the 
tree to force the sap through the pipelines, but 
this was not true. The sap leaks from the 
tissues of the tree under a wide range of pres- 
sures, from very low (almost immeasurable) to 
as much as 40 pounds per square inch. The 
pressure is affected by many factors, among 
which are the temperatures of the air, tree 
bark, and soil. In many runs, and often 
throughout most of a run, sap leaks from the 
tree under very low pressure. Thus, only a 
slight obstruction in a pipeline provides suffi- 
cient back pressure (resistance to flow) to equal 
or exceed the pressure at which the sap is being 
exuded from the tree. Hence, sap flow is pre- 
vented. 

Causes for back pressures (obstructions) in 
the line are (1) gas (vapor) locks resulting from 
pockets of gas exuded from the tree along with 
the sap (8) or from air pockets that result from 
air that has leaked into the tubing around the 



different connections, especially at the spouts 
(through the vent tubes); (2) low places in the 
line where pockets of sap collect, and (3) ice 
plugs of frozen sap. Of these three causes, 
gaslocks are most frequent and may cause 
enough back pressure to support a 5-foot col- 
umn of sap. However, gaslocks can be kept to a 
minimum by careful installation and by provid- 
ing vents to free the trapped gases or air. 

The effect of ice in the pipelines is a contro- 
versial subject. Many believe that by the time 
the air temperature has risen sufficiently to 
cause sap to flow from the tree, the tubing will 
have warmed sufficiently to partly melt the ice 
and allow passage of the sap. Others believe 
that the elasticity of the tubing will permit the 
sap to pass by the ice plug. This is unlikely. Still 
others believe that tubing laid directly on the 
ground, whether snow covered or not, will ab- 
sorb enough latent heat from the earth to melt 
the ice in the tubing before any appreciable 
flow of sap occurs. Ice in tubing installed on the 
ground often melts before ice in tubing sus- 
pended in the air. (This can be observed when 
the two systems are installed in the same sugar 
grove.) There is almost complete agreement 
that ice in tubing layered between two falls of 
snow melts very slowly because of the insulat- 
ing effect of the snow. The tubing must be 
pulled up out of the snow before the ice will 




PN-4739 

Figure AS. — Tubing can be used for a small group of trees 
in an inaccessible area or for roadside trees. 



24 



AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE 



melt and unblock the lines; this is not easy to 
do when the lines are suspended. 

Since maple sap is not exuded from trees at 
all times under high pressure, the best method 
for installing the tubing is one patterned after 
that used in gravity-flow waste-disposal sys- 
tems. These systems are installed with a con- 
tinuous, even though slight, pitch of both the 
feeder lines Qaterals) and main lines toward the 
exit end. Main or trunk lines nuist be of suffi- 
cient diameter so that they are never over- 
loaded. Vents must be installed at all high 
points to prevent gaslocks, and a vent must be 
installed at each spout. 

One of the outstanding features of the plastic 
pipeline is the "closed" system — transparent to 
daylight which minimizes microbial infections 
and keeps the sap clean and free of foreign 
matter (2S, 31). However, infection can and does 
occur; therefore, sanitary precautions must be 
observed in installing and maintaining the sys- 
tem. 

The immediate effects of infection are deteri- 
oration and spoilage of the sap. Since infection 
can be translocated by the moving sap, two or 
more tapholes must not be connected in series. 
This might spread infection from one taphole to 
another (31 ) and prematurely stop sap flow. For 
the same reason, tubing that connects the tap- 
hole to either lateral or main lines must be 
installed with enough elevation between the 
lateral line and the taphole to drain the sap 
away from the taphole freely and completely 
during periods of flow and to provide sufficient 
hydrostatic pressure to insure flow in the main 
lines laid on level ground. 

Installation of flexible plastic tubing Qateral 
or main lines) suspended in the air above the 
ground, free of sags between points of support 
and with a continuous pitch, would be an even 
greater problem than installation of iron pipe. 
A suspension cable would be required. It would 
be stretched from tree to tree above the tubing; 
the tubing would be suspended from it and held 
in a "straight" course by hangers of different 
lengths. In practice, however, sags cannot be 
prevented because fluctuating air tempera- 
tures expand and contract the tubing and cable 
and because the tubing between the hangers is 
not rigid. Also, locating these lateral and main 
lines so that- all tapholes will be a short but 



fixed distance above the main lines U8-50) 
would increase the difficulty of installation be- 
cause numerous main lines and short lengths of 
lateral lines would be required. This system is 
ideal for small installations involving one or 
only a few trees. Do not connect tapholes in 
series except on individual trees. To do so may 
spread microbial infection and stop flow of sap 
prematurely. 

In expanding this system to a large opera- 
tion, the costs of initial installation, takedown, 
and reassembly might be excessive. The system 
does, however, eliminate the need of taphole 
vents, since the short length of the dropline is 
attached to main lines that are not completely 
filled with sap and so will not air-lock. A 
properly installed pipeline system drains itself. 
If sags occur in either ground- or aerial-sup- 
ported systems, pockets of sap will form. These 
pockets cause buildup of back pressures, reduce 
flows, are sites of microbial infection, and form 
ice plugs on freezing. 

Installing Tubing 

There are many methods for installing plastic 
tubing (68, 70). The following method (152) is 
economical of materials and labor, minimizes 
spread of microbial infection, and tends to elimi- 
nate gaslocks and other obstructions that build 
up back pressures in the lines. It provides a 
simple, inexpensive, and satisfactory means for 
installing, taking down, washing, sanitizing, 
and reinstalling plastic tubing. 

Equipment 

Droplines. — Complete assemblies of 5-foot 
lengths (for level land use 6- to 7-foot lengths) of 
^/le-inch inside diameter (I.D.) tubing with a tee 
at one end and a sap spout at the other. The 
spout has a vent tube attached. Vent tubes are 
U-shaped Vie-inch I.D. tubes formed with a 
short piece of wire; they are from 6 to 12 inches 
long and are attached to the vent tubulation of 
the spout (chart 3). The U-shape tends to keep 
micro-organisms out of the system. 

Lateral Lines. — Lateral lines, made of ^/le- 
inch I.D. tubing, connect the droplines to the 
main lines. They are laid on the ground. 

Main Lines. — Main lines vary in size from V2 
to IV2 inches- I.D. 



MAPLE SIRUP PRODUCERS MANUAL 



25 



ALUMINUM WIRE 




VENT TUBE 



^ ID. TUBING 
16 V 



Chart 5.— Vent tube and drop line assembly. 

Spouts. — Spouts have two tubulations, one 
for discharging the sap and the other for vent- 
ing gases. 

Tees and Connectors. — Plastic tees, connect- 
ors, and other fittings of appropriate size are 
required for connecting droplines, lateral lines, 
and main lines. 

Hypochlorite Solution. — A commercial bleach 
containing 5 percent of sodium hypochlorite is 
diluted with water at the rate of 1 gallon of 
bleach to 19 gallons of water. 

Germicidal Pellets. — One germicidal pellet is 
required for each taphole. 

Some producers find it desirable to flush all 
new tubing with a stream of pure water for 10 
to 15 minutes before putting it into use. This 
removes any soluble material in the tubing, 
including that which might produce an off- 
flavor. 



Droplines can be completely assembled at odd 
hours before the sap-flow season. They are 
assembled before they are installed in the 
sugar grove and are not disassembled until 
they need to be replaced. A complete dropline is 
used for each taphole on each tree. 

To install the lateral and main-line tubing so 
that it will have the desired pitch without sags, 
lay out the route it should follow before the sap 
season when the ground is bare and the trees 
along the route have been blazed. Painting the 
trees with vertical lines (blaze marks) will show 
the number of tapholes to be made per tree. 
The paint can be applied in a fine stream from 
a pressure paint can. 

Where the slope of the ground is not too 
steep, it is recommended that a tractor with 
scraper blade be run over the route to level it. 
A short time before the sap season, the trees 
should be tapped and the tubing installed. Al- 
though this can be done by one man, a three- 
man team is more efficient. Not more than 25 
droplines (tapholes) per lateral line should be 
installed. 



V/f 



Li, 



Beginning at a location farthest from the 
storage tank and where two lateral lines con- 
verge, main lines should be laid in the most 
direct route to the storage tank (figs. 44-49). 
Low places should be avoided if possible. The 
first length of the main line should be V2-inch 
LD. The size should be increased as the quan- 
tity of sap entering it increases. On level 
ground, a V2-inch main line will carry the sap 
from 75 tapholes. Where two or more V2-inch 
I.D. main lines converge, they should be at- 
tached to ^/4-inch or 1-inch main lines. These, in 
turn, are connected to still larger main lines as 
the number of converging lines increases. In 
many sugar groves only V2-inch LD. main lines 
are required. 

There is no absolute rule regarding size and 
length of main lines except that they must be 
large enough in diameter to prevent buildup of 
back pressure. Pressure buildup can easily be 
seen by installing 6- foot lengths of ^/is-inch vent 
tubes in a vertical position at the junction 
points. If sap rises in the vent tubes, the main 
line is too small. The carrying capacity of a V2- 
inch main line equals three to four ^/le-inch 



26 



AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE 



lateral lines, and a ^/4-inch main line equals two 
V2-inch lateral lines. 

When a graded course having a uniform 
downward pitch to the tank lines is impossible 
because of the contour of the land, the main 
lines should be suspended from overhead guy 
wires or cables. Suspended installation is espe- 
cially suited for long runs of rnain lines over 
very rough, rocky land, gullies, ravines, and 
valleys. A properly installed main line will 
drain itself. 

Tapping nnd Droplines 

If trees are tapped and droplines are installed 
by a three-man team, the first man locates the 
position for the taphole and bores the hole. He 
sanitizes the bored hole either by syringing it 
with the hypochlorite solution or by inserting a 
germicidal pellet. The second man carries the 
dropline assembly and attaches it to each tap- 
hole by driving the spout firmly into the tap- 
hole. The third man furnishes droplines, hy- 
pochlorite solution, and other supplies to the 
first two men. 




PN-4-41 
unction of several main lines with surge 
tank and vent. 




PN-4-40 

Figure H- — Main line used to transport sap across 
inaccessible area. 



Figure J,6. — Main lines transport sap to storage tank at 
the evaporator house. 



MAPLE SIRUP PRODUCERS MANUAL 



27 




PN-4743 

Figure U7. — Main line to roadside tank for pickup. 

Lateral Lines 

Coils of ^/le-inch LD. tubing are taken to the Figure j,><. 
starting point of installation in the sugar grove, 
usually the storage tank at the roadside or at 
the evaporator house. The laterals are laid out 
and connected by a second three-man team. 

The leadman of the team carries the coil of 
tubing. One of the other men holds the end of 
the tubing. The leadman lays the tubing to the 
first tree tapped. The line should be kept free of 
loops and should lie flat on the gi-ound. The 
tubing is gently pulled to straighten it out and 
the desired length is then cut from the coil. One 
of the other two men holds the cut end of the 
coiled tubing, and the leadman advances to the 
second tree, laying out the tubing as he goes. 
The second and third men alternate in the 
following tasks: Holding the tubing while it is 
being laid out; disinfecting the ends of the 
tubing, tees, and connectors; and connecting 
the laterals to the tees of the droplines. Where 
there are multiple drops (tapholes) on one tree, 
they are connected with 1-foot pieces of */ie-inch 
LD. tubing. 

Laying tubing in shaded areas should be 
avoided. All connections and droplines to later- Figure 1,9. 



f'N-n4j 
-Droplines are installed before ground lines 
are laid out. 




PN-4746 

-The leadman carries the coil of tubing. 



28 



AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE 



als should be on the southern side of the tree to 
favor early thawing of any ice formed in the 
joints (figs. 50 and 51). 

After the tubing has been installed, the en- 
tire system must be checked to insure' that all 
connections have been properly made. Inspec- 
tion tours should be repeated throughout the 
sap-flow season to check for le^ks and sepa- 
rated joints. Inspections are necessary if the 
tubing was installed over deep snow that melts 
during the sap season or if new fallg of snow 
cover the tubing. 

Takinjj Down Tubing 

Tubing must be taken down not later than 1 
week after the last run, or after the trees begin 
to bud. To delay permits growth of micro-orga- 
nisms and makes washing and sanitizing more 
difficult. During the sap-flow season, tempera- 
tures are usually cool enough so that the rate 
of germination of any micro-organisms in the 
tubing is slower than their death rate caused 
by the transmission of ultraviolet radiation of 
sunlight through the tubing. But, as the season 
progresses beyond the budding period, the 





PN-47 4(1 

Figure 50. — Droplines are connected to laterals. 



PN-4747 

Figure 51. — Several laterals are joined to the main line 
with tees or the newly developed collector. 

warmer weather causes the growth rate to 
greatly exceed the death rate of the organisms, 
and abundant growth occurs. Therefore, taking 
the tubing down immediately after the end of 
the season makes the cleaning operation easier. 

The process for taking the tubing down is 
merely a reversal of that described for its in- 
stallation. Like the installation, this process can 
be a one-man operation; but it is more efficient 
when done by two 2-man teams. 

The leadman of the first team at each tapped 
tree disconnects the droplines from the laterals 
and the foot-long connectors, which he collects. 
The second man pulls the spouts from the tree 
and collects the dropline assembly. Disconnect- 
ing lateral lines, short connectors, and drop- 
lines, and tying tubing bundles are shown in 
figures 52-56. 



MAPLE SIRUP PRODUCERS MANUAL 



29 



When 25 droplines have been collected, they 
are tied into bundles, with the tee ends flush. 
Since all droplines are alike, no labeling is 
needed. 




Figure 52.— Taking down droplines. 





Figure 53. — Taking up lateral lines. 



Figure .54.— Tying and labeling bundles of lateral lines. 

The second team collects, bundles, and tags 
the disconnected lateral lines. The leadman 
collects the tubing. Beginning at the first 
tapped tree, he picks up the end of the tubing 
that extends from the main line or storage tank 
and pulls the tube to the second tree. There he 
picks up the end of the tube e.xtending between 
the first two trees and places the end flush with 
the end of the first tube. Then he pulls the two 
lengths of tubing to the third tree and repeats 
the process until a handful of tubing (20 to 25 
pieces) has been collected. Smaller lots may be 
obtained from an isolated section of the sugar 
grove. 

When a handful of tubing has been collected, 
it is left at the tree where the last piece was 
collected. Another member of the team ties the 
flush ends together into a bundle and attaches 
a label showing the general area of the sugar 
grove where it was installed. The bundle of 
tubing is then tied into a coil approximately 2 
feet in diameter for easy handling. 

This system of installing and dismantling the 
tubing not only is simple but makes washing 
and sanitizing of the tubing easy. 

\^a!*liiii<; and .Saiiilizin^ Tiil»iii<£ 

At the end of the maple season most of the 
interior of the tubing is either wet or moist with 
sap. With the warmer weather at that time. 



30 



AGRICULTURE HANDBOOK 134. U.S. DEPT. OF AGRICULTURE 




Figure 55. 



PN-47.'->l 

Coiling lateral lines for ease of handling. 




Figure 56. — Load of tubing to be taken to evaporator 
house for cleaning and storage. 

temperatures are favorable to microbial prrowth 
(yeasts, molds, and bacteria). However, if the 
sap in the tubing: were sterile, either because of 
excellent sanitary practices or because of the 
sterilizing effect of sunlight, no subsequent 
gi'owth would occur. But this seldom, if ever, 
happens. Excessive microbial growth usually 
occurs, especially if higher temperatures follow 



takedown of the tubing. Once gi'owth occurs, it 
becomes increasingly difficult to clean the tub- 
ing. Therefore, the tubing should be washed 
within a few hours after its takedown, and if 
that is not possible, within 1 or 2 days. Tubing 
in which microbial gi'owth is excessive must be 
cleaned by more elaborate methods. 

Etiiiifniiriil 

The following equipment is requii'ed for 
washing the tubing: 

(1) A tank to hold the hypochlorite solution. 
This can be a 55-gallon drum or a stock-water- 
ing tank of approximately 200-gallon capacity. 

(2) A gear-pump that will deliver at least 50 
gallons per hour at 10 to 15 pounds' pressure. A 
bypass arrangement on the pump provides flex- 
ibility of operation. The pump is attached to the 
drain valve of the tank and is equipped with a 
15-foot length of hose provided with a tapered 
nozzle. 

(3) Wash or sanitizing solntioti consisting of a 
10-percent solution of a commercial liquid 
bleach (which contains approximately 5 percent 
of sodium hypochlorite); 20 gallons should be 
used with 180 gallons of water. 

ii) Rubber gloves to protect the hands against 
the caustic action of the sanitizing solution. 



MAPLE SIRUP PRODUCERS MANUAL 



31 



W ashing l.<itfr<ils 

Rubber gloves are worn. A coil of the tubing 
is submerged in the tank of hypochlorite solu- 
tion (fig. 57). The drain valve connecting the 
tank and pump is opened, and the pump is 
started. The stream delivered from the hose 
nozzle is adjusted by means of the pump bypass 
valve. The bundle of tubing is picked up by the 
flush ends. The nozzle is inserted into one of 
the tubes until the tube is completely filled with 
the wash solution (fig. 58). Filling a tube com- 
pletely usually requires less than a minute. 
When air bubbles no longer emerge from the 
discharge end, the tube is completely filled. As 
each tube is flushed and filled with hypochlorite 
solution, it is released so that only the un- 
washed tubes are held. When all tubes in a 
bundle have been flushed and filled with clean- 





PN-n54 

Figure 5S. — After soaking, the tied end of the bundle is 
held and each tube is washed separately. 

ing solution, the coil is allowed to sink to the 
bottom of the tank and another coil of tubing is 
placed in the tank. Then the process of flushing 
and filling each tube of the new coil is repeated. 
This is continued until the tank is filled with 
tubing. 



CAUTION 

Because of the eaiistie action of the 
hypochlorite solution, ruhher gloves must 
Im' Moi-n (luring the Mashing operation. 



PN-4753 

Figure 57. — Coils of lateral lines are submerged in hy- 
pochlorite solution, and all the ties are cut except those 

at the end of the bundle. 



The tubing is soaked for 2 hours; then each 
tube is flushed again, beginning with those in 
the first coil put in the tank. As soon as all the 
tubes in a bundle have been washed, the 
strings holding the bundle in the coil are cut 
but not the string holding the flush ends of the 
tubes. Then, the bundle, held by the flush ends, 
is pulled slowly from the tank (fig. 59). As the 
coil unwinds, the solution in the tube drains 
back into the tank. 

The bundle of tubing is then pulled to a slope 
or laid over the roof of a building to drain (fig. 
60). Thus, the hypochlorite solution is drained 
from the tubing but not washed out. 

After 10 to 15 thousand feet of tubing has 
been washed, the tank should be drained and 
refilled with fresh hypochlorite solution. 

After the bundles have drained for about 2 
weeks, they are taken down and coiled (fig. 61). 



32 



AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE 




Figure 59. — The wash solution drains back into the tank as the tubing is slowly 

withdrawn. 




PN-47r>H 

Figure 60. — The tubes are laid out on an incline or over a 
roof to drain. Here, 12 miles of tubing is being dried. 

Extremely dirty tubing or tubing; with an ex- 
cessive amount of microbial growth should be 
thoroughly cleaned (Hi ). 

For storage, several bundles of tubing from 
the same area of the sugar grove may be 
wound and tied in the same bundle. The coils of 



PN^757 

Figure 61. — The tubing is coiled on a homemade reel, tied 
into bundles for storage. 

tubing are stored in a clean, dark, cool place 
that is free of rodents. Large metal drums or 
tanks with 'Vinch-mesh hardware cloth covers 
make ideal, rodent-free storage containers. 

A bundle of droplines held by both ends is 
lowered slowly and perpendicularly, tee end 



MAPLE SIRUP PRODUCERS MANUAL 



33 



first, into the tank of hypochlorite solution to 
displace the air and to completely fill the tubing 
and fittinfa:s (tees, sjwuts, and vent) with solu- 
tion (fig. 62). Without releasing the bundle, it is 
lifted out of the solution and held in a vertical 
position for a few moments to drain. The ends 
are then reversed and the bundle is again 
lowered into the solution. After the second 
filling the bundle of droplines is left in the tank 
to soak for 2 hours. After the soaking period, it 
is lifted free of the solution and held in a 
vertical position for a few seconds to permit 
most of the hypochlorite solution to drain back 
into the tank. The bundle is then hung by the 
cord ties at the spout end for 2 weeks (fig. 63). 
After draining, the bundle of droplines is taken 



down and stored in the same manner as the 
lateral lines. 

Washitif! Main Lines 

The coils of main lines are washed, drained, 
and stored in exactly the same manner as the 
lateral lines. A larger nozzle is used to fill and 
flush the tubing with the hypochlorite solution. 

Reinstalling Tubing; 

The operation of reinstalling the tubing in 
the sugar grove proves the merit of this system. 
This operation is carried out in practically the 
same manner as that of the initial installation. 

Main Lines 

The cut, clean, large-diameter tubes are laid 
out in the sugar grove in the same manner as 
in the initial installation. 

Droplines and Lateral Lines 

Two 3-man teams are used to reinstall drop- 
lines and lateral lines. The first team drills and 
sanitizes the tapholes and inserts the germici- 
dal pellets, and installs the dropline assemblies 
that have been kept intact in convenient bun- 
dles. 




PN-47SK 

Figure 62. — A bundle uf dicjijlines is lowered slowly and 
jierpendicularly into the wash solution. 



PN-n59 

Figure 63. — The drained droplines are hung in a vertical 
position to dry. 



34 



AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE 



The second team lays out and connects the 
lateral and main lines. The coiled bundles of 
lines are sorted and the one with the label for 
the sugar grove area where the work is to begin 
is selected. The coil is cut apart, and the lead- 
man of the team, holding a bundle by the tied 
flush ends, pulls it to the first tapped tree, 
following- the blaze marks of the preceding year. 
Since each bundle contains tubing of different 
lengths, the second man (who is at the starting 
point at that time) selects the tube that 
matches the distance from the starting point to 
the first tree and pulls it from the bundle. Both 
men now advance. The leadman proceeds to the 
second tree and the second man to the first 
tree, where he again selects a length of tubing 
that matches the distance between the two 
trees. He connects the lateral lines with the 
tees of the droplines. This procedure is repeated 
until the entire grove has been reassembled 
with the droplines and lateral lines. 



siimniarv' 

Plastic tubing can be used for the full opera- 
tion of sap collection and transportation or it 
can be used to perform parts of these opera- 
tions. 

(1) Install plastic tubing as a drainage system 
with proper vents and adequate size tubing 
so as not to restrict sap flow in tubes. 

(2) Do not connect tapholes in series, except 
possibly those on individual trees. 

(3) Lay the tubing on the ground or suspend it. 
Avoid any sags in the lines, and vent these 
whenever they occur. 

Installiufi Tubinn 

(1) Tubing is ground-supported lateral and 
main lines. 

(2) Each taphole is connected to the lateral 
line by a dropline consisting of a spout, 
vent, and 5-foot length of ^/le-inch tubing, 
and a tee connector, preassembled. 

(3) Lateral lines are ^/le-inch tubing cut to fit 
between different trees. 

(4) Make connections of lateral lines and drop- 
lines on warm side of trees. 

(5) Lay the lateral lines along a route of con- 
stant pitch free of sags, previously laid out. 



(6) A 3-man team lays out the lateral line 
most efficiently. 

(7) The number of droplines connected to one 
^/i6-inch lateral line will depend on (a) the 
flow of sap per taphole and (b) the pitch of 
the lateral line. Do not connect more than 
25 tapholes per lateral line. 

(8) A V2-inch main line will cari-y sap from 75 
tapholes (3 laterals). 

(9) Increase the size of the main lines so that 
they are never overloaded. Failure to do so 
will cause back pressure and loss of sap. 

(10) Periodic inspection of the tubing is re- 
quired for leaks. 

Taking Doivn Tubing 

(1) Take the tubing down as soon as possible — 
never later than 1 week after last run. 

(2) Remove all droplines intact, and tie in a 
bundle. 

(3) Keep 1-foot connectors separate. 

(4) Collect lateral lines, keeping the lead ends 
flush in the hand-held bundle. 

(5) Coil and tie for ease of handling. 

(6) Label the bundle at flush ends for the area 
of woods where installed. 

Washing and Sanitizing 

(1) Wash all tubing in a 5-percent hypochlorite 
(bleach) solution. 

(2) Submerge and soak all tubing and fittings 
in hypochlorite solution for at least 2 hours. 

(3) Flush out all tubing as per preceding in- 
structions. 

(4) Keep flush ends of tubing tied in bundle at 
all times. 

(5) Open coiled tubing after washing. 

(6) Lay tubing on incline to drain. 

(7) Hang droplines in vertical position. 

(8) Recoil droplines and mains for storage. 

(9) Store in dark, dry, rodent-free area. 

Rfinstalling Tubing 

(1) Follow the same procedure as initial instal- 
lation: 

(a) Install droplines. 

(b) Connect droplines. 

(c) Lay out lateral lines and connect to 
droplines. 

(d) Connect lateral lines to main lines. 

(2) Lateral lines are laid out according to the 
scheme outlined in text. 



MAPLE SIRUP PRODUCERS MANUAL 

VACUUM SYSTEMS 



35 



The most recent development in collecting 
sap has been the use of vacuum to increase 
taphole flow and facilitate sap transportation in 
plastic tubing and pipeline systems (7, 1,7, 105). 
To utilize vacuum, an unvented or closed tub- 
ing system must be used. The vacuum may be 
created by the flow^ of the sap through the 
tubing due to gravity (natural vacuum) or by 
the use of a pump (pumped vacuum). The best 
vacuum system will depend on the individual 
characteristics of terrain and tree stand for 
each sugar bush. Where an adequate natural 
slope exists, natural vacuum can produce siza- 
ble increases in the yield of sap. The details of 
installing such a system are described by Mor- 
row (73). Gains in sap production are generally 
directly proportional to the amount of vacuum 
in the system, whether produced by natural 
flow or by a pump. As there are many areas in 
the North American maple belt where the slope 



of the land is not sufficient for an effective 
natural vacuum, artificial vacuum systems 
have been developed. Several agencies have 
done research on pumping systems (19, 106). A 
review of the different types of units that can 
be assembled was presented at the Eighth 
Conference on Maple Products (UU). 

It has been well substantiated that vacuum 
markedly increases sap yield. However, the re- 
ports on the use of vacuum emphasize the 
relative complexity of the equipment systems. 
Those wishing to incorporate vacuum, either 
natural or pumped, into their sap collection 
should obtain assistance from someone thor- 
oughly experienced with these systems. County 
agricultural agents in the maple sirup-produc- 
ing areas can recommend sources of expert 
advice on using vacuum and on installing the 
equipment needed in a sap-collection system. 



STORAGE TANKS 



Storage tanks serve the dual purpose of pro- 
viding supplies of sap to the evaporator and of 
storing sap until it can be processed or hauled 
to an evaporator plant. Tanks supplying either 
a farm evaporator or a central evaporator plant 
must hold enough sap for at least 2 days' 
operation. Tanks used as pickup stations must 
be large enough to hold the maximum daily sap 
production of the sugar grove or of the area 
they serve. Pickup tanks used to haul sap from 
the sugar grove or to deliver sap to the evapo- 
rator house must be as large as possible to 
reduce the cost of haulage. 

Wherever possible, locate the tanks so that 
they can be filled and emptied by gravity (figs. 
64 and 65). When this is not possible, motorized 
pumps (electric or gas engine) can be used. 

The tanks should be located in a cool place 
(fig. 66) and not inside the warm evaporator 
house, since warm sap favors microbial gi'owth. 
The tanks should be covered to keep out foreign 
material, and the cover should be clear plastic 
or some other transparent material that will 
transmit the short ultraviolet rays of daylight 
(100). This type of installation is especially 
suited for roadside storage. 



If abovegTound tanks are not emptied fre- 
quently, they should be insulated to prevent 
the stored sap from freezing. Underground 
tanks with opaque covers, although less likely 
to freeze, are difficult to irradiate with ultravi- 
olet light (fig. 67). When the covers of under- 
ground tanks are not transparent to the ultra- 
violet irradiation, germicidal lamps must be 
installed at the top of the tanks to illuminate 
the entire surface of the sap. Underground 
tanks will usually keep the sap at a more even 
(and perhaps at a slightly lower) temperature 
than will aboveground tanks. But since many 
of the bacteria that infect sap gi-ow well at low 
temperatures, underground storage will not 
prevent microbial fermentation and spoilage of 
sap. Even lowering the temperature of the sap 
by adding ice will not prevent this. 

Large storage tanks such as those at the 
evaporator house should also be provided with 
germicidal, ultraviolet lamps to prevent micro- 
bial gi-ovd,h. These lamps should be mounted at 
the top of the tanks above the liquid level and 
arranged so that they will illuminate as much 
of the surface of sap as jwssible. Directions for 
making an inexpensive ultraviolet-irradiation 



36 



AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE 




}'N-4760 

Figure 61,. — The plastic-covered roadside tank should be large enough to hold a maximum daily run and should be 
located so as to permit gravity filling of the collecting tank. 




Figure 65. — This receiving tank is mounted at the road- 
side. Sap is pumped from it to the evaporator storage 
tank. 



Figure 66.— This small evaporator storage tank, mounted 
in the shade, is e.xposed to daylight and covered with 
transparent plastic. 



MAPLE SIRUP PRODUCERS MANUAL 



37 



unit for pasteurizing flowing sap are available 
(AS). 









CAUTION 








€ 


are 


mil 


St be taken nevt 


»r to exp 


ose 


the 


eyes 


to 


ultraviolet 


lamps. 


Lamps 


must 


be 


turn 


e<l 


off when 


worke 


rs are 


in 


or 


around 


the 


tanks. 











Tanks must have easy access for cleaning 
and repair. Workers must be extremely careful 
when working in tanks that have only a man- 
hole opening, so as to be sure they do not 
exhaust the oxygen (ft-esh air) supply and suffo- 
cate. 

Metal or glass-lined tanks such as surplus 
milk tanks are ideal, since their walls are non- 
porous and easy to clean. 

The walls and floor of masonry tanks should 
be smooth and treated with a water-insoluble 
coating to prevent places for microbes to lodge. 
This surface-treating material must be one that 
is approved by the U.S. Food and Drug Admin- 
istration as safe for being in contact with food. 

The tanks should be washed with a detergent 
after each run of sap and the detergent should 
be completely removed from the tanks by using 
at least three separate fresh-water rinses. 

There must be some indicating device inside 
the evaporator house to show the level of sap in 
the tank. This device may be simple sight glass 
(a perpendicular glass tube connected to the 
feed line of the evaporator), or it can be a float- 
and-weight type, where a string attached to a 
float in the tank is carried into the house, and a 
weighted object is raised and lowered by means 
of guides and pulleys as the level of the sap 
varies. 




Figure 67. — A large underground concrete storage tank of 
silo-type construction. 



If the feed line from the tank to the house is 
aboveground, it too must be well insulated. 
Numerous cases have been reported when the 
sap line, even when in operation, has frozen 
and shut off the supply of sap, with the result 
that the pans were burned. 

Suinmarv' 

(1) Construct tanks with smooth, easy-to-clean 
walls. 

(2) Locate tanks in a cool place — never inside a 
warm evaporator house. 

(3) Cover tanks with clear plastic to utilize the 
sterilizing action of sunlight. 

(4) Provide sterile lamps for large tanks with 
opaque covers. 

(5) Provide an indicating device in the evapora- 
tor house to show level of liquid in tank. 

(6) Keep tanks clean and sterile. 



EVAPORATOR HOUSE ON THE SAP-PRODUCING FARM 

Location 



Originally, most evaporator houses were lo- 
cated near the center of the sugar grove to 
shorten the distance the sap had to be hauled 
(fig. 68). With the use of pipelines and large 
collecting tanks, many producers today find it 
more profitable to locate the evaporator house 



near the other farm buildings and close to a 
traveled road (fig. 69). This offers many advan- 
tages: (1) Water and electric power are availa- 
ble; (2) laborious and time-consuming travel to 
and from the evaporator house is eliminated; (3) 
full family participation is encouraged; and (4) 
the evaix)rator house is accessible to visitors 
and potential customers. 



38 



AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE 



Funotiun 

The evaporator house, or sugar house as it is 
often called, like the evaporator, has developed 
without engineering design. In the early days 
of the iron kettle, little thought was given to 
any form of shelter. At first only a lean-to type 
of shed was used to protect both the sirup- 
maker and the boiling sap Ifrom inclement 
weather, which so often occurs during the sirup 
season. The shed introduced a new problem — 
how to get rid of the steam from the boiling sap. 
This problem was solved by completely enclos- 
ing the evaporator and installing ventilators at 
the top. These crude shelters were the forerun- 
ners of today's evaporator houses. 

Since the evaporator house is used only from 
4 to 6 weeks each year, its cost must be kept 
low; otherwise, the interest on the capital in- 
vestment is out of proportion to its use. The site 
should permit use of ramps for filling the stor- 
age tank by gravity (figs. 70 and 71). The house 
should be constructed so that it not only per- 
mits sanitary handling of sap and sirup but also 
provides a place to process and package the 
sirup, to make confections, and to sell maple 
products. 

Requirements 

The evaporator house need not be elaborate. 
It should be large enough to allow plenty of free 





Ife-^-'* 




Figure 68. — Evaporator house located in center of sugar 
grove. Without a covered evaporator, steam completely 
fills the evaporator house. This is unfavorable for sani- 
tary conditions. 



PN-4765 

Figure 69. — The trend is to locate the evaporator house 
near the other farm building-s and on an improved road. 

space (at least 4 feet) on all sides of the evapo- 
rator, and it should be set on a foundation that 
extends below the frostline. The house should 
be tightly constructed and should have provi- 
sions for venting the steam. If open hoods are 
used, there should be intakes to supply air for 
the fire and to replace air that is exhausted 
with the steain. Provision should also be made 
for easy access to the fuel supply and sap 
storage tanks. 

I)esig;n 

Chart 4 shows a suggested plan for an evapo- 
rator house with a wing in which the sirup can 
be processed and maple products can be made. 
The house itself is designed to contain only the 
evaporator and a workbench along one wall. 
The width (16 feet) allows an aisle space of 5 
feet on each side of an evaporator 6 feet wide 
to provide easy access to all parts of the evapo- 
rator. 

.Strain Nontilalion 

In concentrating sap to sirup, vast quantities 
of steam are produced. Without proper means 



MAPLE SIRUP PRODUCERS MANUAL 



39 




PN-4766 

Figure 70.— When possible, select the evaporator house 
site so that the natural elevation will permit building a 
ramp, and sap can be delivered by gravity from the 
hauling tank to the storage tank and from the storage 
tank to the evaporator. 

for removing: it, the steam fills the evaporator 
house and, on cold days with high humidity, the 
inside of the house becomes dripping- wet. In a 
steam-filled evaporator house, the sanitaiy dry 
conditions desired in a food-processing plant ai'e 
impossible (fig. 72). Instead, the wet building 
favors microbial gi-owth. 

The earliest method of removing steam and 
the least effective was to cut a hole in the 



Figure 7;.— When the site is level, the sap can be pumped 
to storage tanks mounted on elevated frames; it will 
then flow by gravity to the evaporator. 

center of the roof directly above the evaporator. 
The hole was the same size as the evaporator. 
The cover for this hole was fastened to the roof 
with hinges on the side of the hole parallel to 
and opposite the ridge of the roof These hinged 
roof sections or louvers were raised or lowered 
by a rope and pulley. The rope was wound on a 
windlass mounted on the wall of the house. 

Tin' Opi'ii llooil 

The next method for removing steam from 
evaporators was the open hood (fig. 73). In this 



.CHIMNEY 



^ STEAM VENT STACK 



WORKBENCH 



SPACE FOR 

SIRUP 

FILTER 

SUGAR KITCHEN 
I2'-0"X 15'- 8" 



REHEATING STOVE 
PACKAGING SPACE 



EVAPORATOR HOUSE APPROX. I6'-0"X 20'-0" 
METAL-LINED HOOD 



SAP STORAGE TANK 
WITH GERMICIDAL 
LAMP 




EVAPORATOR 



-FUEL STORAGE 
-xTANK (UNDERGROUND) 



ChaH 4.— Suggested plan of an evaporator house with "L" to provide space for filtering and packaging sirup and making 

maple confections. 



40 



AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE 




PN_176R 

Figure 72. — Evaporator house with opening in the roof 
for venting the steam results in a steam-filled building. 

method, four walls extending from the rectan- 
gular roof opening to within 6 feet of the floor 
are constructed to serve as a chimney for the 
steam. The walls are sloped so that the lower 
edge projects 1 foot or more beyond the four 
sides of the evaporator. The efficiency of the 
hood is increased by attaching a strip of light- 
weight canvas 1 to 3 feet wide to the lower edge 
of the hood. A small gutter V2-inch deep is 
attached to the lower inside edge of the hood to 
collect water that condenses in it. Since the 
hood has nothing to support, it can be made of 
lightweight, noncorroding material such as 
sheet aluminum. The supporting frame can be 
made of lightweight lumber, and covered with 



aluminum on the inside so that only the metal 
is exposed to the steam. 

This type of hood will keep the evaporator 
house free of steam, but it has many draw- 
backs. Being open, it requires 10 volumes of air 
for each volume of steam removed. Thus, large 
volumes of air must be drawn into the evapora- 
tor house, which makes the house cold and 
drafty. Also, the efficiency of the hood is af- 
fected by wind and by barometric pressure. 
Although the open hood is found in many older 
evaporator houses, it is not recommended be- 
cause it results in unfavorable sanitaiy condi- 
tions. 

Tlip Covered Evaporator 

A simple, effective method for removing 
steam from evaporators is a close-fitting, but 
not airtight, cover from which the steam is 
conducted to the outside of the house through a 
duct or stack (fig. 74). The cover rests on the 
evaporator. This method uses the same princi- 
ple as that used to vent the steam out the spout 
of a boiling teakettle (fig. 75). The method has 
none of the objectional features associated with 
earlier methods. It does not require an exhaust 
fan and it does not raise the boiling point of the 
sirup, since there is no measurable increase in 
pressure within the steam-venting system. 

The cover is made of lightweight, noncorrod- 
ing metal such as sheet aluminum and has a 




PN-4769 

Figure 73. — A canopy-type hood removes steam more 
efficiently than do louvers. However, large volumes of 
air are require<i to sweep the steam into and up 
through the hood and the result is a cold, drafty 
building. 



Figure 7U. — The tight-cover steam-venting system with 
steam stack provides a simple, highly efficient means 
for removing steam. This results in a steam- and draft- 
free evaporator house. 



MAPLE SIRUP PRODUCERS MANUAL 



41 




PN-mi 
Figure 75.— The hot steam causes a natural draft and 
does not require air intake ports. 

light wooden frame of gable design made from 
1- X 4-inch pitch-free lumber (spruce or bass- 
wood). The aluminum sheets are cut to size and 
are attached by aluminum nails to the inside of 
the wooden frame, completely covering the 
wood so that it is not exposed to the steam. 
Galvanized iron should not be used, since the 
acidic gases in the steam will quickly corrode 
and dissolve the zinc coating. 

A satisfactory pitch of the gabled cover is 6 
inches to the foot, or 30°. The walls of the cover 
should be 6 to 8 inches high to provide adequate 
headspace for the free boiling sap. A trap door 
should be placed over the flue (back) pan to 
permit inspection and skimming. However, the 
tight cover has practically eliminated the need 
for skimming. This is no doubt due to the 
absence of air ft-om the steam-filled area above 
the boiling sap. 

The pipes for the stack or steam vent should 
be made of the same lightweight metal, and 
they can be fabricated in any sheet-metal shop. 
The stack should be placed over the flue or sap 
pan, because that is where inost of the steam is 
generated. The stack should be fastened at its 
base to the evaporator cover. It should be long 



enough to extend up to and through a hole in 
the roof of the building to 1 foot above the ridge 
of the roof. 

The opening in the roof should be 1 inch 
larger in diameter than the stack, so that the 
stack can be moved freely. The diameter of the 
stack is not critical; however, it must be large 
enough for the steam to escape readily. Stacks 
of different diameters are required for different 
size covers, as follows: 



Size of cc 


tvered 


evaporator 


Diameter of 
stack ' 


Width (Jeet) Length {feet) 


Inches 


3 




3 


6 


4 
4 




4 I 

5 ( 


8 


3 




'' ) 




5 




" 


10 


3 




10 \ 




4 
6 




I) 


12 


5 

4 




.n 


14 


5 




10 ) 




5 




12 


16 


6 




10 \ 





5 14 I ig 

5 20 I 

' For covers over flue pans use next larger diameter; 
for covers over sirup pans use next smaller diameter. 

For evaporators with two or three sections, it 
is easier to construct separate covers with indi- 
vidual steam stacks for each section. 

To remove the cover, hoist it and the at- 
tached steam stack vertically — push the stack 
up through the roof opening — by means of a 
I'ope attached to eye bolts at each end of the 
ridge pole of the cover. Pass the rope through 
pulleys located overhead and then down to a 
windlass mounted at a convenient height on 
the sidewall of the evaporator house. 

I^ocation of" K\a|><n-ator 

The evaporator should be located directly 
under the ridge of the roof and centered under 
the hood (if an open hood is used). The founda" 
tion for the evaporator arch should be made of 



42 



AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE 



masonry or cast iron. The masonry arch or the 
base of the cast iron arch should extend below 
the frostline and sufficiently high above the 
floor level so that the height of the evaporator 
permits the sap to flow by gi-avity from the 
pans to the filter tank and then from the filter 
tank to the finishing pan. Setting the evapora- 
tor high also makes it easier ^o fire when the 
fuel is wood, and brings the thermometer (for 
checking the boiling point of the sirup) to eye 
level for ease of reading. 

If the sirup is only partly finished in the 
evaporator and evaporation is completed in a 
finishing pan, the finishing pan should be 
mounted adjacent to the evaporator. 

Air Supply 

When the evaporator is in operation, great 
quantities of outside air are required for com- 
bustion of the fuel. For example, 150 cubic feet 
of air per minute is required to burn seasoned 
hard maple at the rate of one-fourth cord per 
hour. If the steam is removed through an open 
hood, an additional 10 cubic feet of air per 
minute per square foot of evaporator will be 
required. For example, an evaporator 4 feet 
wide and 12 feet long requires 480 cubic feet of 
air per minute to remove the steam through a 
ventilator. 

If this air is supplied through an open door or 
window, the evaporator house will be very cold 
and drafty. A more desirable method is to 
deliver air where it is needed. Ducts along both 
sides of the evaporator will supply the hood 
ventilation and the combustion air. These ducts 
should be 8 inches wide and open at the top and 
at the ends toward the firebox. They should run 
the entire length of the evaporator. The air 
coming in through these ducts tends to keep 
the steam under the hood. If the evaporator is 
covered and has a steam vent pipe, the ducts 
will need to supply air only for combustion. 

Siriip-Proressinjj Room 

If the evaporator house is a single room, it 
must have space for filtering the sirup and for 
canning it. It is better to process the sirup in a 
second room built as an "L" to the evaporator 
room (chart 4). This arrangement does not add 
appreciably to the cost of construction and the 



sirup can be processed under better working 
and sanitai-y conditions. 

The processing room houses such operations 
as filtering, heating, and packaging the sirup, 
and making maple confections. The equipment 
consists of a filter rack, a stove for boiling the 
sirup (preferably heated with gas), a maple- 
cream beater, and sugar stirrers. 

There should be a sink for dish washing, a 
hot water heater, and a trough with cold run- 
ning water in which sirup that has been cooked 
for making maple cream can be cooled rapidly. 
Storage space should be provided for cooking 
utensils and containers. 

If the evaporator house is to serve as a 
salesroom, space should be provided for display- 
ing the products attractively and for storing 
the products. 

Fuel Storagje 

When wood is used for fuel, sheltered storage 
must be provided in a convenient location. This 
storage space holds enough wood for a run of 
sap. The supply is replenished from a larger 
storage shed. In some large operations, the 
wood is stored in a separate building and is 
transported to the evaporator house in a truck 
mounted on rails (fig. 76). An overhead tram- 
way can also be used. By installing the tracks 
with a slight downgrade toward the evaporator, 
the heavy loads of wood can be moved by 
gravity. 




Figure 76. — Wood for fuel is conveniently 

separate shed. The wood is moved in a flanged-wheel 
truck that runs on rails to a point adjacent to the 
evaporator. If the storage shed is at a slightly higher 
elevation.'the loaded truck can be moved by gravity. 



MAPLE SIRUP PRODUCERS MANUAL 



43 



Fuel oil storage tanks must be large enough 
to hold enough oil for at least 1 day's operation. 
Larger tanks may lower delivery costs. The 
tanks must be installed to meet local building 
codes. 

Suinniaiy 

(1) If possible, locate the evaporator house on 
the main road close to the other farm 
buildings. 

(2) Build it large enough to provide at least 4 
feet of free space on all sides of the evapo- 
rator. 

(3) Construct it so that it can be kept clean. 

(4) Provide a w^orkbench along one w^all. 

(5) Provide the evaporator with a cover and 
steam vent pipe. 

(6) Elevate the evaporator arch on a founda- 
tion that extends into the ground below 
the frostline. 

(7) Make the floor of concrete or other easily 
cleaned surface. 



(8) Provide ducts in the house for intake of 
outside air. 

(9) Set the evaporator high enough above 
ground to raise the pans a minimum of 4 
feet above the floor. 

(10) If possible, provide a separate but adjoin- 
ing room for processing the sirup and mak- 
ing other maple products. 

(11) If possible, equip the house with running 
water, electricity, and gas fuel supply. 

(12) Provide adequate storage for dry wood or 
oil. 

(13) If wood is used for fuel, provide means for 
transporting the wood to the evaporator. 

(14) Locate the sap storage tanks outside the 
building. 

(15) Cover the tank with material (plastic) 
transparent to the low ultraviolet radia- 
tion of daylight. 

(16) If the tank is enclosed, illuminate the sap 
with germicidal lamps. 



THE EVAPORATOR AND ITS FUNCTION 



The maple sirup evaporator is an open pan 
for boiling water from the sap. Although the 
primary purpose of the evaporator is to remove 
water, it must do the job economically and in 
such a way as to improve but never to impair 
the quality of the sirup being made. 

Maple sirup evaporators have gone through 
an evolution in design. The first evaporator, 
used by the Indians, was a hollowed log in 
which water was evaporated from the sap by 
adding hot stones. The next evaporators were 
metal kettles used by the white settlers. Both of 
these were batch-type evaporators, that is, the 
entire evaporation process, from the first addi- 
tion of sap to the last, was done in one kettle. 
Sap both high and low in sugar content was 
added. It might be many hours before the sirup 
was finally drawn. As a result, a dark strong- 
flavored sirup was produced. 

The next improvement in evaporators was 
the use of multiple kettles (fig. 77). This evapo- 
rator was the forerunner of today's continuous 
evaporators. 

The sap was partly evaporated in the first 
kettle, transferred to the second kettle for fur- 
ther concentration, and then finally transferred 



to a third and sometimes a fourth kettle where 
evaporation was completed. The multiple-kettle 
method was a semicontinuous operation and 
resulted in an improved (lighter colored) sirup 
because the time of heating at near-sirup den- 
sity was shortened. 

The source of heat for all the early evapora- 
tors was an open fire, which is poor in fuel 
economy. 

The first major change in design of evapora- 
tors was the introduction of the flat-bottom pan 
and the enclosed firebox (fig. 78). Both the 
increased heating surface of the pan and the 
confined fire increased the efficiency of the fuel. 
This design was quickly followed by partitioned 
pans, which were the forerunner of flue-type 
evaporators. 

The modern flue-type evaporator, developed 
about 1900, was the next and last major change 
in design. Use of "flues" or deep channels in the 
pans, and altering the firebox so that it arched 
the hot gases between the flues, caused the hot 
gases and luminous flames to pass between the 
flues before escaping up the chimney. Fuel 
economy was increased. Also, the rate of evapo- 
ration was increased, which shortened the 



44 



AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE 




Figure 77. — Multiple-kettle method of making maple sir- 
up. In this method, the sap was partly evaporated in 
the first kettle, then transferred to the second and 
third kettles, and finally to the fourth kettle, where 
evaporation was completed. (Courtesy of W. W. Si- 
monds, Pennsylvania State University.) 




l'N-1774 

Figure 7H. — The flat pan was the forerunner of the 
modern flue pan. 



evaporation time, improved the quality of the 
sirup, and lowered the cost of production. 

Design of Evaporator 

The modern flue-type evaporator, which oper- 
ates under atmospheric pressure, consists basi- 
cally of two sections: (1) The sap pan, in which 
the flues are located, and (2) the sirup pan. The 
sections are separated to facilitate their re- 
moval from the arch for cleaning and repair. A 
semirigid pipe or tubing connects the pans. The 
connections tend to restrict the free movement 
of sap as it travels through the evaporator and 
minimize the intermixing of the dilute sap in 
one pan with the more concentrated sap in the 
adjacent pan. 

So that the evaporators can be operated in a 
continuous or semicontinuous manner, baffles 
or partitions are built in the pans to form 
channels through which the sap flows as it is 
being concentrated. The location of these parti- 
tions and the size and shape of the channels 
differ with different manufacturers. 

The sap pan can be made with narrow, deep 
channels because the sap, while in this pan, is 
never concentrated enough to become viscous; 
it flows readily. Use of narrow flues increases 
the heating surface and thereby increases 
transfer of heat. Fresh sap is admitted to the 
sap pan through a float valve that can be 
adjusted to maintain the desired depth of liquid 
in the evaporator (fig. 79). 

The sirup pan, often called the fi-ont pan, is 
usually located over the firebox. Concentration 
of the sap to sirup is completed in this pan. It 
has a flat bottom to facilitate cleaning and to 
permit evaporation of shallow layers of sirup 
without danger of burning. 

Changes in Sap During Its Evaixji-ation 
to Sirup 

Development of the desired maple flavor and 
color is the result of chemical reactions that 
occur while the sap is boiling in the evaporator. 
(See p. 67.) The extent of these reactions is 
determined in part by the length of time the 
sap is boiled (HI). 

Chart 5 shows the effect of length of boiling 
period on amount of color {150) produced in sap 
of different solids concentrations (" Brix). At low 



MAPLE SIRUP PRODUCERS MANUAL 



45 




Figure 79. — The float valve on the sap pan adjusts tlie 
depth of the Uquid in the evaporator. Different devices 
are used to obtain precise valve settings. 




ORIG, 



BOILING TIME (MINUTES) 



C/iari 5.— Effect of length of boiling period on color forma- 
tion (color index) in sap of different solids concentra- 
tions. 

concentrations little color is produced in a given 
boiling time, whereas at higher concentrations 
more color is produced. The rate of color forma- 
tion does not increase appreciably until the 
Brix value of the sap reaches 25° or more, and 
this occurs after the sap reaches the sirup pan. 
To provide a basis for comparing color of 
maple saps of different concentrations, color is 
expressed as color index. Color index is meas- 



ured with monochromatic light in a spectropho- 
tometer: 

86.3% 



Color index = A 



1 cm 



A.,,„ (86.3/6C) 



where A,-,,, is the observed absorbance at 450 
millimicrons with distilled water used as the 
blank; b is the depth of the solution in centime- 
ters; and c is the grams of solids as sucrose per 
100 milliliters of solution as determined on an 
Abbe refractometer. The maximum color in- 
dices for table sirup of various grades are: 0.510 
for U.S. Grade AA (Light Amber), 0.897 for U.S. 
Grade A (Medium Amber), and 1.45 for U.S. 
Gi-ade B (Dark Amber). 

Other changes that occur in the sap as it boils 
are shown in charts 5 and 6. The rate of color 
formation is greatest as the sap approaches the 
concentration of finished sirup (150). Thus, the 
length of time that sap is heated in the sap pan 
(when the Brix value is low) is relatively unim- 
portant in the formation of color. In the sirup 
pan, however, color develops rapidly as concen- 
tration increases. 

The rate at which water is removed from sap 
at different boiling times and the corresponding 
solids concentration are shown in charts 7 and 
8. 

The curves show that the average time that a 
lot of sap with an initial solids content of 2.5° 
Brix is in the evaporator is approximately IV^ 
hours — a little less than 30 minutes in the sap 
pan and slightly more than 60 minutes in the 
sirup pan. To make high-quality, light-colored 
sirup, the time required to evaporate the sap to 
sirup must be kept to a minimum. Conditions 
that affect the boiling time are: (1) The design 
of the evaporator; (2) the amount of heat ap- 
plied to the evaporator; (3) the efficiency of the 
heat transfer; and (4) the depth of the boiling 
liquid. Once an evaporator is selected and pur- 
chased, the sirupmaker controls only the 
amount and steadiness of heat applied to the 
pans and the depth of boiling sap. 

Evaporation Time 

The evaporation time is measured from the 
time a unit of sap enters the sap (flue) pan until 
it is removed from the sirup pan as sirup. 
Evaporation time should not be measured until 
the evaporator is operating steadily, the heat 



46 



AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE 



1.5 






1.0 


1 Color index ^^ 
\.^- 


s 


0.9* 


/ \ 


® 


o 
- O 


/, 1 , 1 1 1 1 1 1 1 1 L 1 1 1 


1,11 


1 1.5 

o 




// 


1.0 


- 


/ ^ 




Color index ^ 


^ / 
/ 

/ 
/ 


0.5 


f-r-;-rr~~r7 1 1 1 1 1 1 1 


/ 

® 

1 1 1 1 



20 40 60 80 100 

TIME (MINUTES) 

Chart 6. — Changes in Brix value, color, and pH in sap 
during the evaporation period. A, Soon after evapora- 
tion begins the sap becomes alkaline, reaching a pH of 
8 to 9; it then decreases in alkalinity until at the end of 
the period it is about neutral. Little color is produced 
until after the sap reaches a pH of 8, at which point 
color increases at a rapid rate. It increases further as 
the concentration of the sap approaches that of fin- 
ished sirup (30° Brix and above). B, Increase in Brix 
value is slow at the beginning and becomes more rapid 
as evaporation progresses. 

source is constant, the liquid in both the flue 
and sirup pans is in a state of full boil, and the 
sirup is being drawn off at a constant rate or at 
regular intervals. The evaporation (holdup) 
time can be lengthened by increasing the level 
of liquid in the pans. The lowest depth of liquid 
in the evaporator (both pans) will give the 
shortest evaporation time. If the depth of liquid 
is too low, the pans will bum, so this control is 
limited. 

Liquid Level in Evaporator 

The depth of sap to maintain in the evapora- 
tor is determined by a number of factors. Most 
important is the minimum depth that must be 



maintained to keep the pans from burning. 
Many sirupmakers find that a liquid level of 1 
inch in the sirup pan is ideal. When the evapo- 
rator is operating correctly with a steady 
source of heat, there will be a slight gradient or 
decline in the liquid level in the evaporator. The 
highest level will be at the point of sap intake 
and the lowest at the point of sirup drawoff. 
With uneven firing, this gradient is upset. Dur- 
ing periods of low heat, when the sap is merely 
simmering, the gradient is lost. The depth of 
the sap tends to become level, and there is an 
intermixing of sap of different concentrations. 
Intermixing, together with an increase in the 
average depth of sap, results in a longer holdup 
time and the production of darker sirup. The 
lower the Brix value of the sap, the longer the 
holdup time, since there must be greater gra- 
dient in the sap levels. Since the minimum level 
at the point of sirup drawoff is fixed to prevent 
burning the pans, the level at the sap intake 



1- 
z 

LlJ 

LiJ 
Q. 


I 


1 1 1 1 


Z 
< 
Q. 

Q. 60 

< 


-\ 


— 


P4C 





\ 


< 




\ 


5 




\ 


UJ 




\ 


a: 




\ 


2 20 


— 


\ — 


_j 




N. 


o 




>s. 


en 




^^^...^^^ 







1 1 l" — \ 



30 



60 90 

TIME (MINUTES) 



120 



150 



Chart 7. — The average time (time required to remove 50 
percent of the water) that any lot of sap remains in the 
sap pan (see dotted lines) is slightly less than 30 
minutes. The time can be shortened or lengthened by 
using sap of lower or higher solids concentration 
(° Brix), by varying the depth of sap in the evaporator, 
and by varying the intensity of the heat. 



MAPLE SIRUP PRODUCERS MANUAL 



47 




60 90 120 150 

TIME ( MINUTES) 

Chart 8. — The average time (time required to remove 50 
percent of the water) that any lot of sap remains in the 
sirup or front pan (see dotted Hnes) is a little more than 
60 minutes. The time in this pan can also be shortened 
or lengthened by changing the Brix value of the sap 
entering the sirup pan, by varying the depth of the sap, 
and by varying the intensity of the heat. 

must be adjusted to keep the sap proportion- 
ately deeper. A change in the Brix value of the 
sap in the supply tank requires a readjustment 
of the float of the intake valve. Changing to sap 
with a higher Brix value without readjustment 
may result in a burned pan. 

Rates of Evaporation 

The solids concentration of the sap is about 
doubled before it leaves the sap pan, that is, 
nearly 50 percent of the water that is to be 
removed has been evaporated {111, 140). By the 
time the sap reaches a concentration of only 19° 
Brix, 90 percent of this water has been evapo- 
rated. 

The changes in the concentration of a typical 
sap (2.5° Brix) during evaporation are given in 
table 4. 

A two-section evaporator with three channels 
in the sap (flue) pan and four in the sirup (front) 



pan and the points at which the concentration 
was measured (table 4) are shown in chart 9. 
To make 1 gallon of standard-density sirup 

from this sap required , or 34.4 gallons of 

2.5 
sap; 33.4 gallons of water had to be evaporated. 
The solids concentration of the sap was doubled 
(from 2.5° to 5.0° Brix) in the sap pan. This re- 
moved 17.3 gallons of water, or more than 52 

Table 4. — Changes in the solids concentration 
of sap (° Brix) and water evaporated in a 
simulated evaporator, for each gallon of sirup 
produced 





Solids 
concen- 
tration 


Water ev 


aporatec 




Section of 
evaporator 


Per section 


Total 




of sap 














Gal- 


Per- 


Gal- 


Per- 




"Brix 


lons 


cent 


lons 


cent 


Original sap 


2.5 










Sap pan: 












First section ___ 


. 3.0 


5.77 


17.35 


5.77 


17.35 


Second section _ 


_ 3.7 


5.40 


16.24 


11.17 


33.59 


Third section 


. 5.0 


6.16 


18.53 


17.33 


52.12 


Sirup pan: 












Fourth section , 


_ 8.0 


6.45 


19.40 


23.78 


71.52 


Fifth section ___ 


_ 19.0 


6.26 


18.83 


30.04 


90.35 


Sixth section 


_ 42.0 


2.48 


7.46 


32.52 


97.81 


Seventh section 


54.0 


.45 


1.35 


32.97 


99.16 


Finished sirup - _ 


- 65.5 


.28 


.84 


33.25 


100.00 



' Percentage of sugar. 

- When this experiment was conducted, the Brix of 
standard sirup was 65.5°. 



^S\ 




Chart 9. — Top view of a simulated maple sap evaporator 
having 3 channels in the sap pan and 4 channels in the 
sirup pan. Arrow shows direction of sap flow. The solid 
circles show the location of sap of different solids 
concentrations (° Brix), as indicated in table 4. 



48 



AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE 



percent of the 33.4 p:allons of water that had to 
be removed to make 1 gallon of sirup. By the 
time the solids had increased to only 19° Brix, 90 
percent of the water had been removed, and the 
sap had progressed only halfway through the 
sirup pan. Thus, the remaining 10 percent of the 
water was removed in the last half of the sirup 
pan. This shows that most of thf water is evapo- 
rated while the solids are at sufficiently low con- 
centrations to have little effect on the color of 
the sirup. It also shows that sap must be kept 
moving forward through the pan as it ap- 
proaches sirup concentration, so that it can be 
removed from the evaporator as quickly as pos- 
sible. 

This also explains why adding one or more 
sap (flue) pans in a series does not increase 
evaporation time but does increase evaporation 
rate and capacity. Lengthening the evaporator 
system by increasing the number of feet that 
the sap must travel through the different chan- 
nels makes use of the engineering rule that 
evaporation (heat transfer) increases as the 
rate at which the liquid moves over a heated 
surface increases. Thus, lengthening the evapo- 
rator by using supplementary flue pans will not 
increase holdup time; it actually decreases it. 



Therefore, the percentage of solids (weight-vol- 
ume) of the sirup divided by the Brix value of 
the sap equals the number of gallons of sap 
required to produce 1 gallon of sirup. The equa- 
tion is: 

86 

where a = the numberofgallonsofsap to produce 
1 gallon of standard-density sirup. 

X = the Brix value of the sap (to represent 
the solids concentration of the sap). 

Fi"om this number, 1 is subtracted to obtain 
the number of gallons of water that must be 
evaporated from the sap to obtain 1 gallon of 
sirup. The following equation is used: 

86 

Example: With sap having a density of 2.4° 
Brix, 



S6_ 
2.4 



1, or 36 - 1 = 35, 



the number of gallons of water that must be 
evaporated to obtain 1 gallon of standard-den- 
sity sirup. 



Ride of 86 

The amount of water that must be removed 
to reduce the sap to sirup varies with the solids 
concentration of the sap. 

The "Rule of 86" can be applied to determine 
the number of gallons of a particular sap re- 
quired to produce 1 gallon of standard-density 
sirup. The number 86 is used in the calculation 
as representative of the percentage of solids (as 
sugar) on a weight-volume basis that is found 
in a gallon of standard-density sirup. (Until 
1974 the standard density for maple sirup was 
65.5° Brix, and sirup of this density contains 
86.3 percent solids as sugar. Now that the 
standard density is 66.0° Brix, the percentage of 
sugar in a gallon of standard sirup is actually 
87.2, but the traditional "Rule of 86" persists in 
the industry and is quite satisfactory for practi- 
cal purposes.) 

Since the solids concentration of sap is com- 
paratively low, its Brix value and percentage of 
solids (weight-volume) are essentially the same. 



Suniniaiy 

(1) The modern evaporator is an open-pan, flue 
type and has a high evaporation efficiency. 

(2) The major changes that affect sirup quality, 
color, and flavor occur after the sap has 
been concentrated to 45° Brix. 

(3) The development of color and flavor depend 
on the length of time sap with a Brix value 
of 45° or higher is boiled. 

(4) Evaporation rate is increased if the path 
the sap travels over the heated surfaces is 
lengthened. 

(5) Use of multiple sap pans assembled in series 
increases the rate of evaporation. 

(6) The time required for the last stage of 
evaporation is determined by the holdup 
time (depth of sap in evaporator, last section 
or in finishing pan) and the intensity of the 
heat. 

(7) Pi'oduction of light-colored sirup is favored 
by shallow depth of sap in the evaporator 
and by intense constant heat. 



MAPLE SIRUP PRODUCERS MANUAL 

OPERATING THE EVAPORATOR 



49 



Starting the Evaporatoi- 

The sap is run into the evaporator until the 
bottom of the front pan is covered to a depth of 
1 inch; then the fire is lit. As soon as the sap 
begins to boil, the sap inlet float valve is ad- 
justed to maintain the desired depth of liquid 
(V2 to 1 inch) in the sirup pan. As water evapo- 
rates, the float valve admits more sap (fig. 79). 

If sirup has not been made previously, a 
series of adjustments of the float will be neces- 
sary to be sure the liquid in the sirup pan i 
always maintained at a depth of '/., to 1 inch at 
the point of drawoff. 

The constant addition of sap keeps the sap in 
the pan dilute. It becomes progressively more 
concentrated at points farther from the sap 
inlet. The sirup di-awoff is at the farthest point. 

Saps of different solids concentrations (° Brix) 
require different adjustments of the inlet-valve 
regulator to maintain the same depth of sirup 
in the front pan. The depth of sap in the sap 
pan must be gi-eater for sap with a Brix value 
of 1° than for sap with a Brix value of 2° and it 
must be lower for sap with a Brix value of 3°. 
By checking the Brix value of the sap in the 
storage tank, the float valve can be set to 
maintain the desired depth of sap in the evapo- 
rator. The Brix value should be checked with a 
hydrometer every half hour or whenever a new 
lot of sap is run into the storage tank. This will 
prevent burning the pan, which might happen 
with a change to sap with a lower BrLx value 
unless the depth of liquid is increased. 

The pipeline between the storage tank and 
the evaporator must be large enough to assure 
a constant and adequate supply of sap to the 
evaporator, so that a constant level of sap is 
maintained. If this pipe is connected to an 
outside storage tank, it must be insulated to 
prevent the sap from freezing in the line. Were 
this to occur, the supply of sap would be cut off 
and the pans would burn. 

The sap feed line should be equipped with a 
fast-acting valve that can be used to adjust the 
flow of sap and to stop the flow when the 
evaporator is taken out of use. A secondary sap 
feed line should also be installed. This line 
should be equipped with a flexible hose long 



enough to reach any part of the evaporator or 
finishing pan. This is an emergency line for use 
whenever there is a stoppage in the main feed 
line or for quickly supplying sap to any part of 
the evaporator where sap is needed to prevent 
burning the evaporator. 

Drawing Off the Siiiip 

The boiling point of standard-density sirup is 
7° F. above the boiling point of water. This is 
discussed in detail in the section "Elevation of 
Boiling Point," page 72. 

Any thermometer that has a range of 200° to 
230° F. and a sufficiently open scale can be used 
to determine the boiling point of sirup. It 
should be calibrated in V2° and preferably in V4°. 

With older procedures, it was customary to 
make finished sirup in the evaporator. It was 
seldom possible to continuously remove sirup of 
standard density from the sirup pan, except in 
very large evaporators. Instead, the sirup was 
removed discontinuously or in batches. The last 
channel of the sirup pan was in effect a finish- 
ing pan. This caused the following undesirable 
conditions: The sirup channel was seldom iso- 
lated, so that the turbulence of the boiling sirup 
caused a constant intermixing of the finished or 
nearly finished sirup with less concentrated 
sap. This lengthened the holdup time (time sap 
is heated) and occurred when heating is a 
critical factor in flavor and color development. 
Also, each time a lot of finished sirup was 
drawn off, some sirup had to be left in the last 
channel of the evaporator to keep the evapora- 
tor from burning. The sirup that was left was 
then mixed with the next lot of dilute sirup. 
The prolonged heating period darkened the 
color. 

However, when this procedure is followed, 
the drawoff valve must be opened as soon as 
the boiling sirup reaches a temperature 7° F. 
above that of boiling water. The temperature of 
the boiling sirup should be watched closely to 
be sure it neither rises above nor falls below 
this temperature, and the sirup should be 
drawn off at a rate to maintain this tempera- 
ture. If the boiling sirup falls below the proper 
temperature, the drawoff valve should be closed 
immediately. 



50 



AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE 
Finishing Pan 



Because of the difficulties of finishing the 
sirup in the evaporator, use of a separate fin- 
ishing pan is recommended (figs. 80 and 81). A 
separate finishing pan permits (1) complete re- 
moval of the almost finished sirup (45° to 60° 
Brix) from the evaporator, so that there is no 
possibility of intermixing with less concen- 
trated sirup; (2) complete control of finishing 
the sirup without extending the total time the 
sap is heated; and (3) complete removal of the 
finished sirup from the pan. 

The size of the finishing pan is determined by 
the size of the evaporator. Partly finished sirup 
should be removed ft-om the evaporator at least 
once each hour and finished in batches. Since 
sirup transferred to the finishing pan will have 
a solids concentration of not less than 45° Brix 
and since it requires 2 gallons of 45°-Brix sirup 
to yield 1 gallon of 66.0°-Brix (standard-density) 
sirup, an evaporator that has a rated capacity 
of 4 gallons of finished sirup per hour requires a 
finishing pan that holds 8 gallons of 45°-Brix 
sap and provides additional space to take care 
of foaming. A pan 18 inches square will hold 
approximately 1.5 gallons for each inch of 
depth. Therefore, to accommodate 8 gallons of 
45°-Brix sap the pan should be 5 inches deep 
and should have an additional 10 inches for 
foaming. The pan will therefore be 18 inches 
square and 15 inches deep. It should have 
handles and a cover and should be equipped 
with a precision thermometer having a range of 
200° to 230° F. in V2° or preferably V4° divisions 
and a sirup drawoff cock. Preferably, the pan 
should be heated by gas flame since gas heat 
can be easily adjusted and can be shut off when 
the sirup reaches the desired boiling tempera- 
ture. 

For convenience two finishing pans can be 
used alternately. When a finishing pan is used, 
the sap being drawn from the evaporator for 
transfer to the finishing pan need not be of 
constant density. It can be any density above 
45° Brix (3° or more above the boiling point of 
water). The higher the density of the sirup that 
is withdrawn from the evaporator, the smaller 
the amount of liquid that has to be evaporated 
in the finishing pan. 

Another and important advantage of using a 
finishing pan is that it permits filtering the 



m 


m 

mmM. 


1 ' 1 ^ 


H 





PN-4776 

Figure 80. — The finishing pan allows complete control 
over the final stage of the evaporation of sap to sirup. 
Generally, the fuel is bottled gas. 



sirup that is being transferred from the evapo- 
rator to the finishing pan. Sirup at this density 
(45° to 60° Brix) has essentially all of its sugar 
sand (see p. 78) precipitated. At this density, it 
has a viscosity (fluidity) only slightly higher 
than water and filters much more readily than 
does standard-density sirup. 

In some installations, the sirup is pumped 
from the finishing pan to the holding or can- 
ning tank. A cartridge-type filter can be placed 
in this pipeline to serve as a polishing filter. It 
will remove any sugar sand that was not re- 
moved by the major filter or that may have 
been formed in the finishing pan. 

Many producers using bottled gas to heat the 
finishing pan report that the cost of fuel is 
approximately 7 cents per gallon of finished 
sirup. 

A finishing pan is always used in conjunction 
with a complete evaporator (flue pan plus flat 
pan). The flat or sirup pan of the evaporator 
serves as a semifinishing pan. The capacity of 
the evaporator is readily expanded by adding 
one or more flue (sap) pans, each with its own 
arch and separate heat source (preferably oil). 



MAPLE SIRUP PRODUCERS MANUAL 



51 




PN-4771 

Figure 81.— A steam-heated finishing pan, Uke a gas-fired pan, provides positive control of the finished sirup and 

eliminates danger of scorching. 



When a finishing pan is used, the following 
procedures should be observed: 

(1) Do not finish more than 5 to 10 gallons of 
sirup in a batch. 

(2) When the sirup is finished, that is, when it 
reaches the proper temperature (7° F. above 
the exact boiling point of water), heating must 
be stopped immediately. 

(3) Drain all the finished sirup from the pan. 
If any sirup is left in the pan, it will darken the 
next batch. 

(4) Use two finishing pans alternately. 

Aiitoinatic Drawoff 

An automatic drawoff is well suited for draw- 
ing the partly evaporated sap from the evapo- 



rator for later completion in the finishing pan 
(fig. 82). A high precision thermoregulator is not 
required, since a tolerance of ±0.5° F. is accept- 
able. Corrections need not be made for slight 
changes in the boiling point caused by changes 
in barometric pressures throughout the day. 

Automatic valves can be purchased as com- 
plete packages, or they can be assembled as 
indicated in chart 10. These valves are operated 
by a solenoid, which in turn is opei-ated by a 
thermoregulator. The thermoregulator is ad- 
justed by hand to open or close the valve when 
the boiling sirup reaches the desired tempera- 
ture, as measured by a precision thermometer. 

A thermoregulator, if used to control the 
removal of finished sirup from the evaporator 



52 



AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE 



AUTOMATIC SIRUP DRAW OFF 
MECHANICAL ASSEMBLY 



EVAPORATOR PAN 

\ 




THERMO-i 
SWITCH 



5 MICROFARAD 600 VOLT 

OIL-FILLED CONDENSER 

OR TYPE 8A5PS5 (ITT) FEDERAL 

CONTACT PROTECTOR 

FOR 117 V AC OR EQUAL 



Chart 10. — Automatic sirup drawoff. 



or finishing pan, must be sensitive to changes 
of ±0.1° F. The thermoregulator must be recaH- 
brated three times a day. 

When the thermoregulator is operated on 110 
V. a.c, a condenser must be shunted across the 
line (see chart 10) to protect the contact points 
against the surge of heavy current that is set 
up each time the solenoid coil operates. To 
avoid this, it is better to operate the thermo- 
switch on low d.c. voltage and use a high- 
capacity mercury relay to operate the solenoid 
valve. 

Another type of temperature regulator uses 
thermistor probes as the sensing element. A 
sensitive electrical relay must be used w^ith this 
type of regulator, and it is recommended for use 
with the thermoregulator. 

The thermistor probes in the boiling sirup 
must be kept free of sugar-sand deposits. De- 
posits of sugar sand on the probes will change 
their heat-transmitting properties and cause 
error in their response to the sirup boiling 
temperatures. The probes can be kept free of 
sugar sand by soaking them in 10-percent sul- 
famic acid between runs. This same precaution 
applies to the bulb of the thermometer. 

A further advance in controlling automatic 
drawoff has been made at the Eastern Regional 
Research Center (15). A new thermoregulator 



PN-n78 

Figure 82. — The automatic drawoff is especially well 
suited for removing sirup from the evaporator. When a 
finishing pan is used, the evaporator functions as a 
semifinishing pan. 

containing a Wheatstone bridge, thermistor 
probes, and a meter relay automatically com- 
pensates for changes in boiling point caused by 
changes in barometric pressure (fig. 83). The 
instrument employs two thermistor probes. The 
water probe continually responds to changes in 
the temperature of boiling water. The sirup 
probe causes the valve to open whenever the 
temperature of the boiling sirup reaches a pre- 
determined number of degrees above the tem- 
perature of the boiling water — T F. for stand- 
ard-density sirup and slightly more for heavier 
sirup. 

End uf an Eva|K>i'ation 

When the evaporation of a run of sap has 
been completed, care must be taken or the pans 
may be burned. If water is available, it can be 
run into the storage tank as the last of the sap 
is being withdrawn. Little sap will be lost, and 
the pans can be flooded with .3 to 5 inches of 
water before the fire is extinguished. This pre- 
caution is necessai-y when either wood or oil is 
used because enough heat will remain in the 



MAPLE SIRUP PRODUCERS MANUAL 



53 




Figure 8S.— Automatic thermoregulator that compen- 
sates for changes in barometric pressure. 

firebox and arch to melt the solder and the thin 
metal of the pans if the pans become dry before 
the firebox has cooled. 

If water is not available, the fires must be 
extinguished and evaporation stopped while 
there is still enough sap in the storage tank to 
fill the evaporator to a depth of 3 to 5 inches. 

Cleaning the Evaporator 

When maple sap is concentrated to sirup in a 
flue-type open-pan evaporator, the organic salts 
become supersaturated; that is, they are con- 
centrated to a point where they can no longer 
be held in solution. They are then deposited on 
the sides and bottom of the evaporator as a 
precipitate or scale. This scale forms an imper- 
vious layer that builds up with continued use of 
the evaporator. The scale reduces heat-transfer 
efficiency and thus wastes fuel and holds up 
sirup in the evaporator unduly. 

The scale is of two types. One type is a 
protein-like material that forms in the flue or 
sap pans. The other, called sugar-sand scale, 
forms in the sirup or finishing pan. It is a 
calcium and magnesium salt deposit similar to 
milkstone and boiler scale. 

Sugar-sand scale is the more troublesome of 
the two types. It is esi^ecially troublesome if it 
is allowed to build up to an appreciable thick- 



ness. Also, sugar sand contains entrapped cara- 
melized sugar, which contributes to the produc- 
tion of dark-colored sirup. 

Removing sugar-sand scale is not easy, and 
doing it by physical means (scraping, scrubbing 
with steel brushes, or chiseling) is almost im- 
possible. Removal becomes more difficult as the 
layer of scale becomes thicker. Clean the evapo- 
rators often enough to prevent buildup of sugar 
sand. Teflon-coated pans are easier to clean. 
Also, keep the underside of the flues clean. 

Mptlioils I'scd ill file Past 

Some methods used in the past to prevent 
formation of scale and to remove thin layers 
include — 

(1) Reversing the flow of sap through the 
evaporator, according to the manufacturer's 
directions; this retards the formation of scale. 

(2) Running soft spring water through the 
evaporator for a long period; this tends to 
dissolve small amounts of scale. 

(3) Pouring skim milk into the pan and letting 
it remain until it sours; the lactic acid of the 
sour milk has some solvent action on the scale. 

(.Iieiiiirtil (.le<iners 

Equipment manufacturers have used mu- 
riatic acid to remove heavy incrustations of 
sugar-sand scale from evaporators returned to 
them by maple-sirup producers. This acid is 
highly corrosive and must be used with gi-eat 
care to avoid damaging the pans by dissolving 
the thin tinplate coating. Also, unless a person 
is experienced in the use of muriatic acid, there 
is danger that he will get the acid on other 
materials or on his skin. 

Laboratory and field tests have shown that 
sulfamic acid (121), one of the chemicals devel- 
oped for cleaning milk-processing equipment 
and marine boilers, can be used to remove 
sugar sand from most maple sirup equipment. 
Sulfamic acid (the half amide of sulfuric acid) is 
an odorless, white, crystalline solid and is 
highly soluble in water. It must not be confused 
with sulfuric acid. Sulfamic acid crystals can be 
handled easily, with little risk of spilling and 
little danger from volatile fumes. As a solid, 
sulfamic acid is reasonably harmless to the skin 
and clothing. However, a solution of the acid 
can irritate the skin. If either the dry acid or its 
solution comes into contact with the skin, it 



54 



AGRICULTURE HANDBOOK 134, U.S. DEFT. OF AGRICULTURE 



should be washed off immediately with large 
quantities of water. Also, it should be removed 
from clothing and equipment by rinsing repeat- 
edly with large quantities of water. Bulk sup- 
plies should be stored in a tight container in a 
dry place. 

Despite its strong acid characteristics, sul- 
famic acid has only a slight corrosive action on 
most metals except zinc plating, especially if 
contact is for a short period. For example, on 
tin (the metal coating of most evaporators), 
hydrochloric acid is almost 25 times more corro- 
sive than sulfamic acid and sulfuric acid is 
approximately 80 times more corrosive. 

Gluconic acid, another chemical cleaner, is 
recommended for cleaning galvanized-iron 
equipment because it has much less corrosive 
action on the zinc coating. However, use of 
gluconic acid need not be limited to cleaning 
galvanized equipment; it is effective on most 
metals, even though it has a slower cleaning 
action than sulfamic acid. It is usually sold as a 
50-percent water solution. 

Both sulfamic acid and gluconic acid can be 
obtained from suppliers of maple sirup equip- 
ment. 

Use these amounts of acid: 

Sulfamic Acid. — For a thin scale, use V4 
pound (V2 cup) per gallon of water. (This is a 3- 
percent solution.) For a heavy deposit, use V2 
pound (1 cup) per gallon of water. (This is a 6- 
percent solution.) 

Gluconic Acid. — For all deposits, use 1 gallon 
of 50-percent stock solution (obtained from your 
supplier) for each 4 gallons of water. (This is a 
10-percent solution.) 

To avoid damaging the tinned surface of the 
evaporator, do not use a stronger solution than 
recommended; and do not leave the solution in 
the evaporator longer than is required to soften 
the scale. 

Cleaning Procedure 

Use the same methods to clean the flue (sap) 
pans and the sirup (finishing) pan. 

You will need a good supply of piped water, so 
that you can use a hose to rinse the pans. If 
water is not available at the evaporator house, 
take the evaporator pans to a source of piped 
water. 



You should wear rubberized gloves to protect 
your hands from the acid solution. 

The best maintenance practice is to remove 
the sugar-sand scale between each run. The 
following procedure should keep the evaporator 
clean and bright: With a cloth, swab the pans 
with the acid-cleaning solution; allow it to re- 
main a few minutes; then thoroughly rinse the 
pans with water, to be sure the acid is com- 
pletely removed. 

If a layer of scale has accumulated on the 
evaporator, use the following procedure: 

(1) Remove all loose scale and dirt from the 
pan with a broom or brush. Then rinse the pan 
with a good stream of water from a hose. 

(2) Plug the outlets of the pan. If the outlets 
have threaded fittings, use metal screw plugs; 
othei-wise, use wood, cork, or rubber stoppers. 

(3) Fill the pan with water to the level to be 
descaled. Measure the water as you put it in 
the pan, and make a record of the number of 
gallons for future use. Also, make a I'ecord of 
the estimated volume of the pan. 

(4) Add the correct amount of acid to the 
water in the pan. Stir to help dissolve the acid. 

(5) Warm the solution in the pan to a temper- 
ature of 140° to 160° F. This hastens the rate at 
which it softens or dissolves the scale. After the 
warm solution has been in the pan for a short 
time (usually 15 to 20 minutes is enough), brush 
the sides and bottom of the evaporator with a 
fiber brush to speed up removal of the depos- 
ited sand. 

(6) When the evaporator is clean, drain the 
acid from the pan. Turn the pan on its side and 
flush it out with a stream of water. Repeat the 
water rinse five or six times, and allow the pan 
to drain between each flushing. Thorough rins- 
ing is necessary to insure complete removal of 
the acid and its salts from the pan. 

To remove a thin layer of scale with sulfamic 
acid requires from 30 to 35 minutes; to remove 
a thick layer requires from 60 to 90 minutes. 
With gluconic acid, about twice as much time is 
required. The acid solution can be stored and 
reused a number of times. Do not store it in 
iron or galvanized containers; glass or earthen- 
ware containers are best. 

To economize on the amount of acid, use a 
smaller quantity of solution and tilt the pan 



MAPLE SIRUP PRODUCERS MANUAL 



55 



first in one position and then in another until 
all the scale-covered surfaces have been soaked. 
Sulfamic acid and its salts are toxic to grow- 
ing plants. For this reason, it is an effective 
weedkiller. But care should be taken not to 
discard the used acid solution where desirable 
plants may be damaged or killed. 

Endrof-Senson Cleaning 

A much-used procedure for cleaning evapora- 
tor pans at the end of the season is to fill them 
with sap and let them stand several weeks. The 
sap will ferment and the acids formed will 
loosen the scale. If the sap becomes ropy and 
jellylike, it will be difficult to remove. However, 
if it is allowed to stand longer, it will again 
become liquid and can be removed easily. As 
with the other cleaners, the pans must be 
rinsed after the fermented sap treatment and 
dried before they are stored. Fermented sap 
will not remove heavy scale deposits. 

Whether to clean the evaporator at the end of 
the sap season is debatable. Some producers 
store the evaporator pans with the deposit, 
assuming that this serves as a protective coat- 
ing and keeps the evaporator surfaces from 
corroding. The preferable method is to clean the 
equipment so that it is ready for use the next 
spring. In either case, the evaporator pans 
should be dried and stored in an inverted posi- 
tion. 

Smninaiy 

(1) Use a flue-type open-pan evaporator as the 
basic unit. 

(2) Evaporate more than 90 percent of the 
water in the evaporator. The sap should 
have a Brix value of 45° to 60°. 



(3) Complete the evaporation in a finishing 
pan. 

(4) To expand the evaporation, add one or 
more flue pans and operate them in series. 

(5) Operate the evaporator with a minimum 
depth of sap. Keep the depth of sirup at 
point of drawoff at V2 to 1 inch. 

(6) Keep sap boiling vigorously at all times. 

(7) For wood fires keep the fire uniform and 
keep the fire doors closed except when 
adding fuel. 

(8) If a finishing pan is not used, draw off the 
sirup as soon as it reaches the proper 
boiling temperature (7° F. above the boil- 
ing point of water for that hour and place). 

(9) If a finishing pan is used, draw off the 
sirup at 45° to 60° Brix (boiling tempera- 
ture at drawoff 2.5° to 5.1° F. above the 
temperature of boiling water). Use an au- 
tomatic valve controlled by a thermo- 
switch. 

(10) Filter the sirup in transferring it from the 
evaporator to the finishing pan. 

(11) As soon as the temperature of the boiling 
sirup in the finishing pan rises 7° F. above 
the boiling point of water (which yields 
standard-density sirup; 7.5° above the boil- 
ing point yields 67°-Brix sirup with better 
taste), immediately stop heating, cover the 
pan and withdraw the sirup. 

(12) Clean the evaporators often enough to pre- 
vent buildup of sugar sand. 

(13) Rinse the evaporator pans with large 
amounts of water (use three separate rin- 
ses, draining the pan between each rinse 
after each time a chemical cleaner is used 
in the evajwrator or finishing pan). 

(14) Keep the underside of the flues clean. 



OTHER T^ PES OF EVAPORATORS 



Other types of evaporators include the steam 
evaporator (or a combination of oil and steam) 
and the vacuum evaporator. 

Stoain Evaporator 

The evaporation of maple sap with high- 
pressure steam (figs. 84-86 and chart 11) is 
practiced by a few producers {97). Its use, how- 
ever, has never become widespread. Steam 



evaporators have several advantages, as fol- 
lows: (1) The heat is steady; therefore, the sap 
can be evaporated at a continuous and even 
rate. (2) Heat can be supplied in steam coils, 
manifolds, or a jacketed kettle. (3) The evapora- 
tor can be constructed with smooth walls; flues 
are unnecessary. (4) Scorching of sirup is mini- 
mized. (5) The evaporator room can be sepa- 
rated from the boiler room, which makes it 



56 



AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE 




PN-4780 

Figure 8J,. — High-pressure steam boilers are economical 
when low-priced fuel is available. Approximately 20 
gallons of finished sirup per hour can be made in the 
two 100-h.p. boilers shown. 





Figure 86. — This evaporator consists of several units 
connected in series with the partly evaporated sap 
moving successively to the next evaporator by means 
of a float control to prevent intermixing of concen- 
trated sap with less concentrated sap. 



easier to keep clean. (6) The high-pressure 
steam can be used as the source of heat in 
making a variety of maple products. (7) Where 
soft coal can be obtained cheaply, high-pressure 
steam is economical. 

The disadvantages of steam evaporators are: 
(1) A license may be required to operate a 
steam boiler. (2) The boiler needs periodic in- 
spection and overhauling. (.3) In some areas the 
water is not suitable for use in a steam boiler. 
(4) The initial cost of the steam boiler may not 
be justified. 

The approximate size of a steam boiler (boiler 
horsepower, b.h.p.) required to evaporate sap to 
sirup can be calculated, since 1 b.h.p. will evapo- 
rate approximately 3.25 gallons of water (sap) 
per hour. The value 3.25 varies slightly, depend- 
ing on the temperature of the sap as it enters 
the evaporator and the operating pressure of 
the boiler. As indicated earlier, 33.25 gallons of 
water must be evaporated from sap with an 
initial Brix value of 2.5° to produce 1 gallon of 

/ 33.25 * 
sirup. Approximately 10 b.h.p. 



3.25 



will be 



PN-nsi 
Figure 85. — A converted evaporator that uses high-pres- 
sure steam coils with steam generated by two 100-h.p. 
boilers. 



required to produce 1 gallon of sirup per hour. 

A system that is proving successful is the 
combination of oil and steam. In this two-stage 
system, oil is used to concentrate the sap to 
about 30° or 40° Brix in flue pans, and steam is 



MAPLE SIRUP PRODUCERS MANUAL 



57 



HIGH PRESSURE 
STEAM SUPPLY 



^ LARGE VAPOR VENTS ^ 




REMOVABLE 
^COVERS 

3 PARTITIONS 
IN FINISHING PAN 



STEAM TRAP 



CONDENSATE RETURN 



FLOAT VALVE IN BOX 
ON EACH UNIT 



DRAW -OFF VALVE 

■FILTER BOX 



FINISHED SIRUP 



Cha)i 11. — Multiple-unit steam evaporator. 



used to complete the evaporation. This combi- 
nation has all the advantages of steam for 
finishing the sirup, but requires a smaller, and 
therefore less expensive, steam boiler. 

Va<'iiiiiii E\u|>«>rator 

Milk-concentration or fruit-juice evaporation 
plants in maple-producing areas can be adapted 
for evaporating maple sap. This was done dur- 
ing the 1930's at Antigo, Wis., where a milk 
plant was used to make sirup during part of the 
day in the spring sirup season (3). 

The procedure used at Antigo is as follows: 
The sap is concentrated to between 25° and 30° 
Brix in the conventional open-pan evaporator 
at the farm site. This is 90 percent of the 
required evaporation. Evaporation is completed 
in a vacuum evaporator at the central sirup- 
finishing plant. This two-stage method of evap- 
oration results in a nearly colorless and flavor- 
less maple sirup. Such sirup is not marketed for 
direct use, but it is ideal for the production of 
high-flavored sirup, as described on page 106. 



A study at Cornell (42) showed that the use of 
milk-plant equipment during off-jieak seasons 
for evaporating maple sap was practicable but 
that the sirup pi-oduced had to be treated by 
the high-flavoring process to obtain marketable 
maple sirup. The fixed costs for use of milk- 
plant equipment are negligible. However, the 
perishable, partly concentrated sap must be 
transported to the milk-concentrating plant, 
and use of a central sirup-finishing plant re- 
quires a new procedure for maple-sirup produc- 
tion. 

Siimiiiaiy 

(1) The steam evaporator provides a steady 
source of heat, and danger of scorching is 
minimized. The sirup produced is light col- 
ored and delicately flavored. However, the 
steam evajwrator is expensive to install. A 
combination oil-and-steam system (two- 
stage method of evaporation) is proving suc- 
cessful; it has all the advantages of steam 
but is less expensive to install. 



58 



AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE 



(2) The vacuum evaporator, which is Hmited to 
large-scale or central-plant operation, is 
used to complete the evaporation of sap that 
has been partly concentrated on the farm. 



The equipment used usually is idle milk- 
evaporation equipment. The sirup produced 
has essentially no maple flavor, but it is 
excellent for use in making high-flavored 
sirup. 



FUEL 



Wood 



The modern flue-type evaporator was de- 
signed for burning wood. A wood fire carries a 
luminous flame throughout the entire length of 
the arch. The flue area of the evaporator and 
the part that lies over the firebox are heated 
both by radiant and by convection heat liber- 
ated by the burning gases. The wood may be 
sound cordwood, defective trees removed in 
improvement cuttings, or sawmill wastes — 
either culls or slab (69). 

In the evaporation process, the object is to 
evaporate the water in the shortest possible 
time. Therefore, it is essential to use only diy, 
sound wood that will produce a hot fire. Wet or 
green wood will not produce as much heat as 
will the same volume of dry wood. Poor burning 
fuel results in a slower boiling rate. This, in 
turn, causes the sap to be held in the evapora- 
tor for a longer time and results in a darker 
sirup. 

A steady fire shortens the boiling time. The 
best results are obtained by charging the fire- 
box first on one side and then on the other, 
keeping the fuel in the firebox at almost con- 
stant volume (fig. 87). The fire doors should be 
closed immediately after each charging to re- 
duce the intake of cold air which cools the 
underside of the pans. When this happens, the 
boiling rate of the sap decreases and holdup 
time in the evaporator increases. Likewise, ash- 
pit draft doors that are open too wide will admit 
more air than is required for combustion, and 
the excess air has a cooling effect. Introduction 
of cold air beneath the evaporator pan in either 
the firebox or the flue area not only reduces the 
boiling rate but also tends to set up counter 
currents in the flowing sirup in the different 
channels of the evaporator. This also contrib- 
utes to the production of a darker sirup. 

Based on $25 per cord of wood, the fuel to 
produce a gallon of sirup would cost about $L 



This represents about 10 percent of the cost of 
sirup production (5, 113). The heating values of 
different wood fuels expressed in British ther- 
mal units (B.t.u.'s) for a standard 4- by 4- by 8- 
foot cord are maple, 22,800,000; beech, 
20,900,000; and hickory, 24,800,000. 

oa 

The advantages offered by using oil as the 
heat source for evaporating maple sap to sirup 
are numerous (lOi). Chief among these are (1) it 
is automatic; therefore, it does not require the 
services of a fireman; (2) it provides a steady 
uniform heat, which is desirable for producing 
high-quality sirup; (3) it is clean and therefore 
aids in better housekeeping and sanitation in 
the evaporator house; and (4) in terms of Brit- 
ish thermal units, the cost of oil at 35 cents per 




PN^783 

Figure S7.— When both doors are opened for firing, the 
excess air admitted chills the pan. Boiling stops; sap 
and partly evaporated sirup intermix; and then, when 
the fuel is again burning briskly, the evaporator must 
equilibrate itself. 



MAPLE SIRUP PRODUCERS MANUAL 



59 



gallon is more than double the cost of wood at 
$25 per cord, but the operational costs may not 
differ greatly since oil does not require the 
services of a fireman. 

The disadvantages of using oil as the fuel 
source, while few, are nevertheless important: 
(1) The initial cost (capital investment) of oil 
burners is high; (2) oil burners require a special 
arch (firebox) although in a new installation it 
is not necessarily more expensive than the 
conventional wood-burning arch; and (3) oil 
does not make use of the cull trees that must be 
removed each year from a well-managed sugar 
bush. 

When oil is used as fuel, two pertinent facts 
must be observed. The first and most important 
is that wood and oil burn in different ways. 
Wood burns with a luminous flame (long fire 
path) throughout the length of the evaporator, 
including the area under the flue pans as well 
as under the sirup pan; oil, on the other hand, 
burns as a ball of flame in only a relatively 
small space. Secondly, of the two forms of heat 
transfers — radiant and convection — used in a 
sap evaporator, radiant heat accounts for ap- 
proximately 80 percent of the heat transfeiTed 
to the liquid, whereas convection heat (that 
which is derived from the hot flue gases passing 
over the surface of the pans and flues) supplies 
approximately 20 percent. Therefore, to make 
use of the radiant heat from the oil fire, the ball 
of burning oil must illuminate the entire under- 
surface of the pans. This necessitates properly 
positioning the ball of burning oil and eliminat- 
ing any obstructions that will prevent illumina- 
tion of the entire undersurface of the pans. This 
requirement will be met only through the 
proper design of arches made for the burning of 
oil as fuel. 

A wood-burning arch cannot be successfully 
converted to an oil-burning arch without major 
changes. The principal fault of such a conver- 
sion is that the slope of the wood-burning arch 
behind the firebox does not permit illumination 
of the entire underside of the sap or flue pan by 
the ball of burning oil and, consequently, the 
sap will not boil. 

Size of Burner 

The size of burner to use is determined by 
two factors: (1) The length and width of the 



evaporator (the vertical area of the flues has a 
minor effect) and (2) the quantity of sap to be 
evaporated per hour. If the rated capacity of 
the evaporator in gallons of sap per hour is 
known, it can be divided by 13 (the approximate 
number of gallons of water evaporated per hour 
by 1 gallon of oil) to obtain the size of burner 
(g.p.h. = gallons of oil per hour) required for a 
specific evaporator. 

The rated capacity of an evaporator burning 
wood cannot be accurately equated to that of 
an evaporator burning oil. Therefore, this 
method of calculation may indicate a burner 
that is too large. However, this is not serious 
since the amount of oil burned per hour can be 
changed, within limits, by changing the size of 
the nozzles. 

To prevent damaging the pan by firing with 
an oversize burner, it is recommended that for 
the first trials a nozzle size 20 percent smaller 
than indicated by the above calculation be used. 
The burning rate (nozzle size) can then be 
increased as needed. An empirical method for 
determining nozzle size is to divide the surface 
area (length times width) by .5. Thus, a 5- by 12- 
foot evaporator would require an oil burner 
nozzle of 12 g.p.h. 

Tyite of Burner 

With few exceptions, high-pressure oil burn- 
ers that use No. 2 oil are recommended. They 
are available with different nozzle sizes to fit 
evaporators of all sizes. Their lower initial cost 
offsets any advantage gained by using burners 
that require the heavier grades of oil. 

Muniber of Burners per Arch 

Only one burner is required for each evapora- 
tor (fig. 88). It must be correctly positioned 
under the evaporator and the combustion 
chamber must meet certain minimum stand- 
ards. Use of a single burner reduces the capital 
investment and installation costs. For example, 
the capital investment and installation costs for 
an evaporator requiring 12 gallons of fuel per 
hour supplied by a single burner would be 
approximately half that for an evaporator sup- 
plied by two 6-gallon-pei--hour burners. In addi- 
tion, the two smaller burners will require more 
servicing and attention than will the larger 
one. 



60 



AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE 




PN-4'H.l 

Figure S8. — A correctly positioned, single, high-pressure, 
domestic-type burner will give the required heat for the 
evaporation of the sap. 

If one burner is used, it should be mounted 
far enough below the bottom of the pan so that 
the radiant heat will be effective across the full 
width of the pan. If construction of the arch 
does not permit mounting the burner this far 
below the pan (see table 5), then two or more 
smaller burners mounted horizontally should 
be used to insure heating the full width of the 
pan (fig. 89). If the slope of the arch is such that 
the undersurface of the flue pan cannot be 
illuminated by the ball of fire (see chart 12), 
boiling may not occur in the area not illumi- 
nated. This is especially true of wood fuel 
arches that have been converted for oil burn- 
ers. To compensate for this, a supplementaiy 
firebox can be constructed under the flue pan. 
and another burner mounted; however, this is 
not always satisfactoiy. 

\ftzzh' Tip 

For evaporators in which the length is ap- 
proximately twice the width, the nozzle tip 
should be at an 80° angle. For evaporators in 
which the length is greater than twice the 
width, the nozzle should be at a 60° angle. 
Irrespective of the type of nozzle tip or the 
angle, the burner must be adjusted so that the 



PN-47S5 

Figure 89. — When one large burner cannot be mounted 
sufficiently far below the pan, two or more .smaller 
burners can be mounted horizontally to give the re- 
quired amount of heat without danger of producing hot 
spots. 

correct amount of air is fed along with the 
atomized oil to insure complete combustion. 
This can be checked with a flue gas analyzer. 



Arvh 



,1 ( 



ihiisti 



( h 



The arch for oil fuel also serves as a support 
for the evaporator pans and contains the com- 
bustion chamber and the flue for the hot gases. 
The arch should be located in the evaporator 
house to provide an adequate working space 
with room for installing supplemental arches as 
the operation is expanded. The arch need not 
be in the center of the evaporator house but 
may be at one side. The concrete footings for 
the arch should be on gravel and should extend 
below the frostline. An all-masonry arch, with 
external walls built of cinder block or brick, 
may be built on the site, or the arch may be 
prefabricated with exterior walls of sheet metal 
on a cast iron and steel frame. In either case, it 
must conform to certain minimum dimensions. 
The interior construction is similar for both. 

Dinu-nsioiia <>/ trr/i.— The size (length and 
width) of the arch is determined by the size of 
the evaporator. It must be wide enough to 
support the pans and long enough not only to 
support the pans but also to hold the base of 
the flue-gas stack. Chart 12 shows a masonry 
arch for a 5- by 12- foot evaporator (9- foot flue 
pan and 3- foot flat pan). The outside walls are 



MAPLE SIRUP PRODUCERS MANUAL 



61 



Cinder till, may have 
I" fire brick facing 



Combustion chamber 
Insulating fire brick 
(2800° F, ) 



— Cinder brick 



Firebrick, 
zS'V X 4'/2" X 9" 




LONGITUDINAL SECTION T i i T T I i CROSS SECTION 

Chart ;^.— Arch and firebox for oil-fired evaporator. 



cinder block except for the top section, which is 
3V2-inch bricks to provide a 2-inch supporting 
surface for the pans and project IV2 inches 
beyond the pans. If the arch is made to the 
exact outside dimensions of the pans, the sup- 
porting wall of the arch would cover too much 
of the underpan surface (3V2 inches on all sides). 
A large loss of heating surface would result. 

The height of the ai'ch is governed by the size 
of the combustion chamber, which in turn is 
governed by the size of the burner (see table 5) 
and the size of the evaporator. For a 5- by 12- 
foot evaporator, the height of the arch should 
be 46 inches (chart 12). The arch should elevate 
the pans 46 inches or more above the floor level 
to permit the use of gravity flow of the sirup in 
successive operations. If the arch raises the 
pans too high, especially when multiple evapo- 
rators are used, a catwalk can be installed; or 
the combustion chamber of the arch and the 
burner can be built in a pit. 



Firebox and (.ombustioii Chamber. — The 

entire open space enclosed by the arch under 
the pans is the firebox. Better results will be 
obtained if it contains a combustion chamber 
(see chart 12). The function of this chamber is 
(1) to provide a hot radiating surface and (2) to 
utilize the hot, incandescent surface to vaporize 
and insure complete combustion of the oil. 

For maximum efficiency, the size of this com- 
bustion chamber must conform to minimum 
dimensions that are related to the nozzle size of 
the burner. These dimensions are given in table 
5. A rule-of-thumb relation between combus- 
tion chamber and nozzle size is that there 
should be a floor area of 90 square inches for 
each gallon per hour of rated nozzle capacity. 

The distance between the top of the combus- 
tion chamber and the bottom of the pans (di- 
mension D of chart 12) is important for two 
reasons: (1) The ball of burning oil should be far 
enough below the "cold" pan surface to prevent 



62 AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE 

Table 5. — Inside dimensions of combustion chamber and stack diameters 



Distance 
from center 
burner 
Burning rate of draft tube 
oil (g.p.h.) to combus- 
tion cham- 
ber floor 
(A) 



Minimum 
height 



(B) 



(C) Distance 

between 
Length for nozzle combustion 



angle of- 



chamber 
and top 
of arch 

(D) 



(E) 



Width for nozzle 
angle of — 



80° 



Approxi- Minimum 

mate floor diameter of 

area stack 



Inches inches 

5 9 18 

6 9 18 

7 10 19 

8 11 19 

9 11.5 19 

10 12 19 

12 13 20 

14 14 21 

16 15 22 

18 16 23 

20 17 24 

22 18 25 

24 19 25 



Inches Inches 



Inches Inches 



25 
27 
29 
30 
32 
33 
36 
39 
41 
44 
47 
49 
51 



21 
23 
25 
26 
28 
29 
32 
35 
37 
40 
42 
44 
46 



Square 

inches 

450 

540 

630 

720 

810 

900 

1,080 

1,260 

1,440 

1,620 

1,800 

1,980 

2,160 



Inches 
10 
10 
10 
12 
12 
12 
12 
14 
14 
16 
18 
20 
20 



corrosive deposits on the underside of the pan; 
and (2) the ball of fire must be far enough below 
the pan so that the acute angle of radiation 
from the apex (ball of fire) to the extreme sides 
of the pan is kept to a minimum (table 5). If the 
ball of fire is too close to the pan, there is 
insufficient space between the pans and the top 
of the combustion chamber; and the angle of 
radiation becomes too great. This results in 
uneven heating across the width of the pan. 
Overheating occurs directly over the fire. This 
can be compensated for only by using more 
than one burner mounted horizontally. 

Construction of Arch and I'onibiistion 
C.httmher 

Arches may be made of sheet metal or ma- 
sonry (chart 12). In arches made of either mate- 
rial, the combustion chamber is free standing 
within the arch and is constructed of insulating 
firebrick. In sheet-metal arches the remainder 
of the arch is lined with hard firebrick. The 
combustion chamber is separated from the ex- 
terior wall of the arch by an air space to allow 
for expansion of the heated bricks. For the 
same reason, there is an air space between the 
hard firebrick liner and the exterior walls of the 



arch. The fill between the combustion chamber 
and the rear of the arch must be of a nonpack- 
ing material such as cinders. 

Size of Stack 

Since the oil burner is operated under forced 
draft, the flue stack need not be as high or as 
wide as when wood is the fuel. The size of the 
stack is governed by the size of the oil burner 
(table 5). 

With only one arch, it is recommended that a 
complete evaporator, flat pan, and flue pan be 
used. However, it is also recommended that the 
flue pan be at least two-thirds the total length 
of the evaporator. The flat pan serves as the 
semifinishing pan in which the sap is raised to 
a density of 55° or 60° Brix. The partly concen- 
trated sap should be transferred from the evap- 
orator to the finishing pan where the final 
stage of evaporation is completed. Although sap 
can be concentrated to sirup in the evaporator, 
this practice is not advised. 

Installation of Multiple Arches 

To increase the capacity of the evaporator, 
additional arches and pans can be added. Each 
additional arch should be equipped with a flue 



MAPLE SIRUP PRODUCERS MANUAL 



63 



pan only and should be installed ahead of and 
in series with the complete evaporator (see 
chart 13). The supplemental flue pan arches are 
constructed in exactly the same manner as the 
one for the complete evaporator. To connect the 
supplemental flue pans in series with the evap- 
orator requires only one point at which the raw 
sap is fed and one point at which the partly 
evaporated sap or sirup is removed for transfer 
to the finishing pan or bottling tank. In the 
multiple unit assembly, the flat pan of the 
evaporator continues to serve as the semifinish- 
ing or finishing pan (fig. 90). 

Efficiency af Heat 

A study of the use of oil as fuel for the 
evaporation of maple sap in an open evaporator 



was reported by Phillips and Homiller (87). 
They showed that commercial maple sap evapo- 
rators fired with oil haye an efficiency of 66 to 
74 percent. Their data were obtained with a 
smaller-than-average evaporator; larger evapo- 
rators would be expected to be slightly more 
efficient. The efficiency of the open pan evapo- 
rator compares favorably with commercial 
steam generating plants, for which a combus- 
tion efficiency of 80 percent is considered good. 
The efficiencies obtained by Strolle and oth- 
ers (111) in evaporating 45 to 55 gallons of 3°- 
Brix sap to standard-density sirup are given in 
table 6. These data indicate that efficiency de- 
creases as the rate of sap feed (gallons of sap 
evaporated per hour) increases and that oil cost 
per hour also increases. However, from further 




Figure 90.— In one of the most economical and efficient types of evaporators, an oil fire and four fine pans are used for 
evaporation; high-pressure steam is used for the last stage of evaporation. 



64 



AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE 



FLOW DIAGRAM 
OF MULTIPLE UNIT EVAPORATOR 



OIL 
FIRED 




FINISHING PAN 
(GAS FIRED) 



TO 
POLISHING FILTER 
AND CANNING TANK 

Chart 13. — Flow diagram of multiple-unit evaporator. 

calculations and rough extrajX)lations the data 
in table 7 were obtained. 

These data show that sirup production in- 
creases as the amount of fuel burned increases. 
The increase in cost of fuel per gallon of sirup is 
slight and is more than compensated for by the 
improvement in the gi-ade of the sirup and the 
reduction in evaporation time and cost of labor. 



Table 6. — Efficiency of oil-fired experimental 
evaporator in evaporating sap of 3° Brix to 
standard-density sirup 



Sap evaporated per 
hour (gallons) 



Oil burned per 
hour 



Efficiency 



45 
50 
55 



Gallons 
3.9 

4.7 
5.3 



Percent 
74 
69 
66 



Table 7. — Extrapolated efficiency of oil-fired 
evaporator 



Sap evapo 
rated per 

hour 
(gallons) 



Cost of 
Oil Sirup oil per 

burned made gallon of 
per hour per hour sirup 
produced 



Time re- 
quired to 
evapo- 
rate 550 
gallons 
of sap 



Effi- 
ciency 



Galloyis Gallons Dollars Hoiirs Percent 



65 6.7 

60 6.0 

55 5.3 

50 4.7 

45 3.9 



2.36 1.00 8.5 59.6 

2.18 .96 9.2 62.6 

2.00 .93 10.0 66 

1.82 .91 11.0 69 

1.64 .84 12.2 74 



The maximum efficiency that could theoret- 
ically be obtained from an oil-fired evaporator 
would utilize all the British thermal units 
(B.t.u.'s) of a gallon of oil. This heat would raise 
the temperature of the feed sap to its boiling 
point and then vaporize the water in the sap to 
steam. Assuming that the temperature of the 
sap is 35° F. and its boiling point is 210°, the 
heat (B.t.u.'s) required to evaporate 34.4 gallons 
of sap with a density of 2.5° Brix to yield 1 
gallon of standard-density sirup can be calcu- 
lated. Knowing the B.t.u.'s of No. 2 fuel oil 
(139,000), the number of gallons of oil required 
to produce this gallon of sirup at maximum 
efficiency is 2.2 gallons. Since no oil burner is 
100-percent efficient, and oil-fired evaporators 
are only 60- to 75-percent efficient, the fuel 
required per gallon of sirup is 3+ gallons of oil. 

To measure the efficiency of burners, arches, 
and evaporators, a number of factors must be 
carefully obtained. These are: 



MAPLE SIRUP PRODUCERS MANUAL 



65 



(1) The Brix Value of the Raw Sap.— For 
example, only half as much water is evaporated 
from 3°-Brix sap as from a lV2°-Brix sap to 
make standard-density sirup. Therefore, other 
things being equal, it would require only half as 
much oil to make sirup from 3°-Brix sap as from 
lV2°-Brix sap. 

(2) Temperature of Sap. — The temperature of 
the sap as it enters the evaporator must be 
noted, since a great deal of heat is required just 
to heat the sap from its storage temperature to 
its boiling temperature. Therefore, the warmer 
the sap, the less oil required to heat it to 
boiling. 

(3) The Brix Value of the Finished Sirup.— AW 
too often the exact Brix value of the finished 
sirup is not considered in making efficiency 
studies. Yet a difference of only a few tenths of 
1° in Brix value has a pronounced effect on the 
number of gallons of sap that must be evapo- 
rated to produce the sirup. 

For cost accounting records, most producers 
will find that merely to divide the number of 
gallons of sirup made by the number of gallons 
of oil burned will give the fuel costs per gallon 
of sirup. These data should be considered an 
estimate of the efficiency of the oil-burner in- 
stallation. 

The cost of fuel oil can be kept low by con- 
tracting for it through competitive bidding. The 
heat (B.t.u.'s) produced by one cord of wood is 
approximately equivalent to that produced by 



175 gallons of oil. The efficiency of wood de- 
pends on many variables, such as condition of 
the wood, size of the individual pieces, how it is 
fired, condition of the fire, and stack height. 

Summary' 

(1) Wood 

(a) Use only well-seasoned dry wood, either 
cord or slab. 

(b) Keep a steady fire. 

(c) Fire first on one side of the firebox, then 
on the other. 

(d) Keep the fire doors ojien only long enough 
to charge the firebox. 

(e) Ojjen the dampers and draft doors only 
enough to furnish the air for combustion. 

(2) Oil 

(a) Oil is recommended if there is a shortage 
of labor. 

(b) The firebox and arch must be specially 
built. 

(c) The cost of fuel for making sirup is ap- 
proximately the same for oil and wood. 

(3) Increase the capacity of the evaporator 
through the addition of one or more sap or 
flue pans. 

(4) Mount the supplemental pans on their indi- 
vidual arches. 

(5) Hook up the supplemental arches in series 
with the evaporator. 

(6) Use a finishing pan. 



MAPLE SIRUP 



The characteristics of maple sirup are dis- 
cussed here so that the development of color 
and flavor will be better understood. 

(Composition of Sap and Sirup 

Table 8 gives the composition of maple sap 
and sirup. The analyses in this and later tables 
are not average values; they are analyses of 
typical saps and sirups. Usually the sirup and 
sap have essentially the same composition, ex- 
cept that on an "as is" basis the constituents of 
the sirup show a thirtyfcld to fiftyfold increase 
as a result of concentrating the sap to sirup. 
The amounts of some of the constituents, when 
expressed on a dry-weight basis, are less in 



sirup than in sap because of their removal from 
solution as insoluble sugar sand. 

The different kinds of sugar in maple sap are 
not numerous (91). Sucrose, the same sugar as 
in cane sugar, comprises 96 percent of the dry 
matter of the sap and 99.95 percent of the total 
sugar (table 9). The other 0.05 percent is com- 
posed of raffinose together with three unidenti- 
fied oligosaccharides. Un fermented sap does 
not contain any simple or hexose sugars. 

The sap contains a relatively large number of 
nonvolatile organic acids (table 10), even 
though they account for only a small proportion 
of the solids (89). The concentration of malic 
acid is 10 times that of other organic acids. If 



66 



AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE 



Table 8. — Composition ofynaple sap and 
sirup ' 



Sap 



Sap (dry Sirup (dry 
weiRlit) weight) 



Percent Percent Percent 

Sugars 2.000 97.0 98.0 

Organic acids .030 ^1.5 .3 

Ash .014 ".7 .8 

Protein .008 .4 .4 

Unaccounted for __ .009 .4 .5 

' Typical values, not averages. Maple sap and sirup 
vary in composition between rather wide limits. 



Table 9. — Siigars in maple sap and sirup 



Sugars 


Sap 


Sap (dry 
weight) 


Sirup (dry 
weight) 


Hexoses 

Sucrose 

Raffinose and a 


Percent 
_ 
. 1.44 

^ .00021 

.00018 
.00020 
.00042 


Percent 


96.00 

.014 

.013 
.014 
.028 


Percent 

0-12 

88-99 


glycosyl sucrose _ 
Oligosaccharides: - 
I 




II 




III 









' Typical values, not averages. 

■ The oligosaccharides have been isolated by chroma- 
tography but have not been identified. 



may prove to be useful in detecting adultera- 
tion (151). One or more of these acids may be 
important in forming "maple flavor." Sap con- 
tains soluble ligninlike substances that are in- 
volved in the formation of maple flavor (117). 

The ash or mineral matter (table 11) accounts 
for only 0.66 percent of the whole sirup, or 1 
percent of the dry solids. Although the minerals 
are only a minor part of the sirup, they have 
been useful in establishing the purity of maple 
sirup and they contribute an astringency to the 
sirup that many find desirable. 

Calcium, a part of the ash, is responsible for 
the sugar-sand scale, calcium malate, which 
forms on the pans (18). The low sodium and 
high potassium content of the ash suggests the 
use of maple in dietary foods. 

Composition of sugar sand ranges as follows 
U8): 



Range 

Sugar sand in run percent__ 0.05- 1.42 

pH 6.30- 7.20 

Ca percent-. 0.61-10.91 

K do 0.146-0.380 

Mg do 0.011-0.190 

Mn do — _ 0.06- 0.29 

P .... do 0.03- 1.18 

Fe p.p.m... 38-1,250 

Cu p.p.m._. 7- 143 

B p.p.m..^ 3.4- 23 

Mo p.p.m... 0.17- 2.46 

Free acid percent-^ 0.07- 0.37 

Total malic acid do 0.76-38.87 

Acids other than malic do 0.08-2.62 

Undetermined material do 6.94-34.16 

Calcium malate do 1.30^9.41 

Sugars in dried samples do 33.90-85.74 

Sugar sand in dried samples do 14.26-66.09 



Table 10. — Nonvolatile organic acids in maple 
sap and sirup ' 



Acid 



Sap 



Sap (dry 
weight) 



Sirup (dry 
weight) 





Percent 

0.021 

.002 

.0003 

.0003 

.000 

Trace 



Percent 

1.40 

.13 

.02 

.02 

.L«0 

Trace 



Percent 
0.141 


Citric 


.015 
.012 




.006 


Glycolic or 

dihydroxybutyric- 

Unidentified acids: 

I, II, III, IV 

V, VI, VII 


.006 

Trace 
Trace 


' Typical values, not 


averages. 







Table 11. — Mineral composition of maple 
sirup ' 



Item 


Sirup 


Diy weight 


Soluble ash 

Insoluble ash ... 


Percent 

0.38 

.28 


Percent 

0.58 

.42 


Total ash ... 


.66 


1.00 


Potassium 

Calcium 


.26 
.07 


.40 
.11 


Silicon oxide 
Manganese 


.02 

.005 
.003 


.03 

.008 
.005 


Magnesium 


Trace 


Trace 


' Typical values, 


not averages. 





MAPLE SIRUP PRODUCERS MANUAL 



67 



The nitrogenous matter constitutes only a 
small part of the total solids (88).'' Expressed as 
nitrogen, the sap contains only 0.0013 percent 
and the sirup 0.06 percent. The sap does not 
contain any free amino acids except late in the 
sap-flow season. Nitrogen occurs only in the 
form of peptides. Whether the nitrogenous mat- 
ter enters into the formation of maple color or 
flavor is an open question. An increase in free 
amino acids is associated with the development 
of "buddy sap." 



FORMATION OF TRIOSES 
FROM SUCROSE 



HYDROLYSIS OF SUCROSE 



C|2 HjjO,, 
(SUCROSE) 



FISSION OF HEXOSES 



(HEXOSES) 
► Cg HiaOe + CsHjOg 
(GLUCOSE) (FRUCTOSE) 



(.olor anti Flavor 

Maple sap as it comes from the tree is a 
sterile, ciystal-clear liquid with a sweet taste. 
None of the brown color or flavor that we 
associate with maple sirup is in the sap. This is 
easily demonstrated by collecting sap asepti- 
cally, freezing it, and then freeze-drying it. The 
solid obtained is white or very light yellow and 
has only a sweet taste. The typical color and 
flavor of maple sirup are the result of chemical 
reactions, involving certain substances in the 
sap, brought about by heat as the sap boils 
(H8). Since at least one of the products of the 
reaction is the brown color, it is known as a 
browning reaction. Neither the exact nature of 
this reaction nor the identity of the reacting 
substances is known. Indications are that one 
or more of the 6 sugars or their degradation 
products and one or more of the 12 organic 
acids in maple sap are involved in the browning 
reaction. 

Experimental evidence indicates that the 
color and flavor of maple sirup are related to 
triose sugar {52-5J,, 118-120, 122, 155). These 
sugars are not constituents of sap when it 
comes from the tree but are formed as a result 
of the two reactions shown in chart 14. Evi- 
dence also indicates that the phenolic ligninlike 
substances of maple sap are intermediate in the 
flavor reactions and may account for the speci- 
ficity of maple flavor (117). 

The amount of invert hexose sugars is di- 
rectly proportional to the amount of fermenta- 
tion that has occurred. The first reaction is the 
bacterial or enzymatic hydrolysis of the sucrose 
to form invert sugar, a mixture of fructose and 



GUUCIC ACID 




TRIOSE n 



ACETOL 



'Also unpublished data of Eastern Regional Research 
Center. 



Chart li. — Chemical reactions showing the formation of 
trioses from the sucrose of sap. In the first reaction, 1 
molecule of sucrose is hydrolyzed by enzymes to yield 2 
molecules of hexose sugars. In the second reaction, 
these hexoses are broken by alkaline fission into 
trioses. 

dextrose (chart 14). The second reaction is the 
alkaline degradation of the fructose and dex- 
trose to trioses (98). The second reaction occurs 
while the sap is boiling in the sap pan, where 
the alkalinity of the sap reaches a pH of 8 to 9. 
These trioses are highly active chemically. 
They can combine with themselves to form 
color compounds, and they can react with other 
substances in the sap (such as organic acids) to 
form the maple flavor substances (79). 

Experiments have established that up to a 
point the amount of color formed is proportional 
to the amount of flavor formed. This makes it 
possible to evaluate flavor in terms of color, a 
measurable quantity. When the point is 
reached at which the background flavor "cara- 
mel" begins to be noticeable, this relation no 
longer holds. 

The identity of the compounds responsible for 
the flavor of maple has proved to be elusive. 
Certainly all the components of maple sirup 



68 



AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE 



contribute to its flavor — the sugar, the organ it- 
acid salts, and even the oil, butter, or whatever 
was used as an antifoam agent during evapora- 
tion. An unknown number of trace materials in 
the sirup or sugar give it "maple flavor." These 
compounds have defied identification for many 
years because they exist in very small amounts 
(a few parts per million), and their chemical 
character in many cases is so similar to carbo- 
hydrates that separation from the sugars of the 
sirup has been extremely difficult (123). Now 
with the modern techniques of gas chromatog- 
raphy and mass spectrometry, progress is being 
made in solving the mystery of "maple flavor." 
The flavor compounds identified can be divided 
into two groups according to their probable 
source. One group, possibly formed from lig- 
neous material in the sap, contains such com- 
pounds as vanillin, syringealdehyde, dihydro- 
coniferyl alcohol, acetovanillone, ethylvanillin. 
and guaiacyl acetone. A second group, most 
likely formed by caramelization of the carbohy- 
drates in the sap, includes acetol, methylcyclo- 
pentenolone (cyclotene), furfural, hydroxymeth- 
ylfurfural, isomaltol, and alpha-furonone (25, 
116). It has been impossible to make a synthetic 
maple flavor by combining these compounds. 
Perhaps one or more key compounds have not 
yet been identified. Even if all these compounds 
were available, a proper balance of the many 
parts of a mixture to give the desired combina- 
tion flavor would be difficult to achieve since 
they have not been accurately measured. 

Factors that control color and flavor are: (1) 
Amount of fermentation products in the sap 
(75)\ (2) pH of the boiling sap; (3) concentration 
of the solids (sugars); (4) time of heating (time 
necessary to evaporate sap to sirup); and (5) 
temperature of the boiling sap (la, 150). The 
two most important factors are the time of 
heating and the amount of fermentation prod- 
ucts in the sap (150). The temperature of the 
sap under atmospheric pressure (open pan) boil- 
ing is fixed, and nothing can be done about it. 
Neither can anything be done about changes in 
pH of the boiling sap. At the beginning of 
evaporation, the natural acidity of fresh sap is 
lost and the sap becomes alkaline. It is during 
this alkaline phase of the pH cycle that hexose 
sugars, if any are present, undergo alkaline 
degi-adations. The sap then remains alkaline 



until sufficient organic acids are formed by the 
decomposition of the sap sugars to make the 
sap acid again. 

The longer the boiling time, the darker the 
sirup; and, conversely, the shorter the boiling 
time, the lighter the sirup. During evaporation, 
the effect of the boiling-point factor increases 
as the solids concentration of the sap increases. 
The relation between the amount of hexose 
sugars (invert sugar) produced during the fer- 
mentation of the sap and the length of time the 
sap is boiled is of the greatest importance. 
Thus, the color and flavor of sirup made in 
exactly the same boiling time from a series of 
saps of equal solids concentration (Brix value) 
but with increasing amounts of invert sugar 
will be progressively darker and stronger. The 
stronger maple flavor, however, is usually 
masked by the acrid caramel flavor. Although 
flavor and color are formed because of exo- 
thermic chemical reactions, the amount of fla- 
vor that can be produced is limited by the 
concentration of the sap-soluble lignaceouslike 
materials that are probable flavor precursors. 
Indications are that there are sufficient of 
these flavor percursors in sap to permit forming 
a product that is from 15 to 30 times richer in 
maple flavor than is commercial "pure maple 
sirup" (15i). These precursors can be utilized to 
increase the flavor by subjecting the sirup to 
higher temperatures. This method is used in 
preparing high-flavored maple products, de- 
scribed later. 

Buddy Sap and Sirup 

As the maple tree comes out of dormancy, 
physiological changes in the tree form constitu- 
ents in the sap which, when boiled, give off a 
noxious odor and impart a characteristic, un- 
pleasant flavor to the sirup. This noxious odor 
is most noticeable in sap obtained from trees 
whose buds have swelled or burst during a 
period of warm weather; and sirup made from 
this sap is said to have buddy flavor. Due to the 
unseasonably warm weather in 1963, buddy sap 
was produced early in the sap season. Because 
of this, much of the crop was not harvested in 
some areas. Although the trees may not have 
come far enough out of dormancy to cause the 
buds to swell, they may have come out enough 



MAPLE SIRUP PRODUCERS MANUAL 



69 



to produce the unwanted flavor. The formation 
of this buddy substance is accompanied by an 
increase in the free amino acids in the sap. 
Whether this parallel increase in free amino 
acids is involved in the foi-mation of buddy 
flavor remains to be determined. 

Often some trees in a sugar grove "bud" 
earlier than the rest. These trees should be 
identified and marked so that their sap will not 
be collected late in the season. To combine the 
sap from trees that have budded with that from 
the other trees would spoil the entire lot of late- 
season sap. 

The practice of treating the taphole with 
germicidal wllets will cause the sap to flow late 
in the season and when the tree is far enough 
out of dormancy so that the sap is buddy. 
Test for Buddy Fhivor 

It is essential that sap produced during or 
following a warm spell or from trees whose 
buds have swelled be tested for buddiness 

The best and simplest test is easily performed 
by bringing V4 cup of the sap or sirup to be 
tested to a boil and sniffing the steam. If the 
buddy flavor substances are present, they can 
be detected in the steam. The sap or sirup can 
be heated with an electric immersion-type 
heater used for making instant coffee. This test 
is subjective, and the buddy odor may not be 
strong enough to be easily recognized by some 
people. 

Another test that is applicable to sirup and 
not subjective has therefore been developed. 
This test involves the chemical test for amino 
acid groups whose presence in sap parallels 
buddy flavor formation (115). 

To make the test the following equipment is 
needed: 

A 1-ounce (30 ml.) screw-cap bottle to hold the 
standard amino niti'ogen solution. 

A box of wooden toothpicks. 

Test papers — filter paper cut into ^/a- x 4- inch 
strips. 

The following reagents should be used: 

Standard amino nitrogen solution. This is 
made by dissolving .5 grams of leucine (an 
amino acid) in 30 milliliters of water. 
(Place 1 level teaspoon of leucine in the 1- 
ounce bottle and fill it to the neck with 
water.) 



Ninhydrin spray. This is commercially availa- 
ble as an aerosol spray. 
The test should be made as follows: 

(1) To a small volume of the sirup to be te.sted, 
add an equal volume of water and mix thor- 
oughly. 

(2) With a pencil make three dots 1 inch apart 
down the center of the test strip, 1 inch from 
either end. Label X, S, and W. 

(3) Holding a toothpick in a vertical position, 
dip the broad end into the diluted sirup and 
transfer a drop to the pencil dot at the top of 
the paper labeled X. 

(4) Using fresh toothpicks, transfer a drop of 
the standard amino nitrogen solution to the dot 
at the center of the paper labeled S, and a drop 
of water to the dot at the bottom labeled W. The 
size of the wetted spots should be about the 
same. 

(5) Lay the paper on a clean, diy surface 
(piece of filter paper) and allow the spots to dry 
at room temperature. 

(6) Spray the entire paper strip with the 
ninhydrin reagent. Wet the paper thoroughly 
but not enough to cause the reagent to run. 

(7) Dry the sprayed paper at room tempera- 
ture. 

(8) Heat the paper at a temperatui-e of 175° to 
195° F. for approximately 1 minute to hasten 
development of the color. The lid of a boiling 
kettle or other moderately hot surface will suf- 
fice. (From 1 to 2 hours will be required for the 
color to develop at room temperature.) 

(9) Development of a violet color constitutes a 
positive test and indicates that the sap is 
buddy. 

The standard amino nitrogen solution is used 
to indicate that the ninhydi-in reagent is react- 
ing properly to give violet color with amino 
compounds. 

Ninhydrin reagent is a very sensitive stain. 
Care must be taken to keep the paper test 
strips clean. Handling the test strip with for- 
ceps, especially after staining, will prevent fin- 
gerprints which could produce false-colored 
spots. The papers are best sprayed by hanging 
them in an open cardboard box to prevent 
discoloration of other objects by the ninhydrin 
spray. The ninhydrin i-eagent is not stable and 
should be replaced at least every 6 months. 



70 



AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE 



Always start with a fresh supply of the reagent 
at the beginning of each sirup season. 

Rcrlaiininff Buddy Sirup and Sap 

Many sirupmakers make buddy sirup from 
the late runs of sap. Although this practice 
should not be encouraged because of the very 
low price commanded by buddy sirup, it is 
made — often unknowingly. ^ 

Buddy sap and buddy sirup can be treated by 
a fermentation procedure to remove their un- 
palatable flavor {136, 137). Because this process 
requires special equipment and a high degree of 
technical conti'ol, it has not been commercially 
successful. Recently a new procedure has been 
developed using ion-exchange resins to remove 
the buddy off- flavor (36a). This process removes 
the amino acids believed to be responsible for 
the buddy flavor of maple sirup. The cost of this 
treatment on a commercial scale is estimated to 
be less than $1 per gallon of sirup. 



Riilo of Sirupinakin^ 

The following rules should be followed in 
sirupmaking: 

(1) If possible, test all sap for buddiness; but 
especially test that produced late in the spring 
or following a warm spell. Do not use buddy 
sap. 

(2) Do not use fermented sap. To keep the sap 
from fermenting, collect it often. Do not allow it 
to stand in the buckets or tanks, and keep it 
cold. If there is a small flow of sap that does not 
warrant collecting, dump it. At least once dur- 
ing the season, wash the sap-gathering equip- 
ment (buckets, pails, and tanks) and sanitize 
the equipment with a 10-percent hypochlorite 
solution. 

(3) Handle the sap as quickly as possible. The 
sooner sap is evaporated after it has been 
obtained from the tree, the higher the grade 
and the lighter the sirup that will be produced. 
The faster sap is evaporated to sirup, especially 
during the last stages of evaporation when the 
solids concentration is highest, the lighter the 
color and the higher the grade of the sirup. 

(4) Keep sap and equipment clean. Cleanli- 
ness is a must in maple sirupmaking for, aside 
from its esthetic aspects, cleanliness is the only 
way to control microbial contamination and 



subsequent growth in the sap. Sirup made from 
sap in which growth of micro-organisms has 
occurred tends to be dark colored and low in 
grade. 

(5) By means of a hydrometer or other suita- 
ble instrument, measure and record the sugar 
content of the sap produced by each tree and 
also the sugar content of each batch of sap in 
the storage tanks. 

(6) Store sap in a cool place. 

(7) Store sap in tanks exposed to daylight (not 
necessarily direct sunlight). 

(8) Cover the tanks with material transparent 
to ultraviolet radiation, such as clear plastic. 

(9) Provide tanks having opaque covers with 
germicidal lamps. 

Grades of Sirup 

It is generally believed that the best sirup is 
made early in the season during the first and 
second runs of sap. However, this is not neces- 
sarily true, as was demonstrated in 1954 when 
sirup made early in the season was darker than 
some made later. The important factor is the 
atmospheric temperature. Warm weather favors 
microbial growth, and the byproduct of this 
growth — invert sugar — affects the color and 
grade of the sirup. It is only coincidental that 
the weather is usually cooler at the beginning 
of the season and microbial growth is low. 

Sap that is essentially sterile contains very 
little invert sugar and will usually produce a 
light-colored, light-flavored, fancy sirup. Some- 
times, as in 1954, the weather at the onset of 
the season is warm, and fermentation occurs. 
The result is that the first-run sirup is darker 
than expected. If conditions are reversed later 
in the season, fancy sirup will be produced, for 
with cold weather little or no fermentation of 
the sap occurs. 

Making light-colored sirup with sterile sap 
that is veiy low in invert sugar does not test a 
sirupmaker's skill. However, skill is required to 
produce light-colored sirup from sap rich in 
invert sugar (with a high microbial count). This 
skill is actually a measure of how fast the 
sirupmaker can evaporate the sap to sirup. 

Sirup can be darkened — changed from U.S. 
Fancy to U.S. Grade A, or from U.S. Grade A to 
U.S. Grade B, etc.— by prolonging the heating 



MAPLE SIRUP PRODUCERS MANUAL 



71 



of the finished sirup. If a finishing pan is used, 
it should be covered immediately when the 
sirup reaches the correct density. The heat 
should be reduced to maintain a slow boil until 
the desired color is obtained. Adding V2 cupful 
of U.S. Grade C sirup for every 2 gallons of sap 
will hasten the darkening process. 

SuiTunar\ 

(1) Maple sap and sirup contain only sugar, 
protein, organic acids, ash, and less than 2 
percent of material not accounted for but 
which is of great importance because it 
includes the color and the flavor substances. 

(2) Sterile maple sap has neither color nor fla- 
vor. 

(3) Experimental evidence indicates that the 
color and flavor in maple sirup are related 
to triose sugars, organic acids, and soluble, 
ligninlike substances. 



(4) Factors controlling the formation of color 
and flavor include fermentation, pH, solids 
concentration, length of boiling time, and 
the boiling temperature of the sap. 

(5) The shorter the boiling time, irrespective of 
the quality of the sap, the lighter the color 
of sirup produced. 

(6) For best sirup — 

(a) Use sap that has not fermented. 

(b) Use speed in collecting and in evapo- 
rating the sap. 

(c) Keep equipment clean. 

(d) Know the initial Brix value of the 
sap. 

(7) Higher grades of sirup are usually produced 
earlier in the season than later on, because 
the early season temperatures are usually 
lower and there is less chance of fermenta- 
tion. 

(8) Sirup that is too light can be darkened by 
heating the finished sirup. 



CONTROL OF FINISFIED SIRUP 



Finishing the sirup is one of the most exact- 
ing tasks in maple sirupmaking. The sirup must 
be drawn from the evaporator or finishing pan 
at just the right instant; otherwise, its solids 
content (density) will be either too high or too 
low. To conform with minimum Federal and 
State requirements, sirup must have a density 
of not less than 66.0° Brix at a temperature of 
68° F. At this density, a little more or a little 
less evaporation has a relatively large effect on 
the concentration (table 12). Hence, when using 
large evaporators capable of evaporating sev- 
eral hundreds of gallons of water per hour, 
accurate control of the sirup being drawn off is 
both important and exacting. 

Viscosity of Maple Sii-up 

Maple sirup having a density of only 0.5° to 1° 
Brix below standard-density sirup tastes' thin. 
This is due to the big change in the viscosity of 
sugar solutions caused by only a slight change 
in concentration, especially in the range of 
standard-density sirup. 

Table 13 shows that an increase in the sugar 
concentration of sucrose solutions up to 30° 
Brix has little effect on viscosity. For example. 



a solution with a density of 20° Brix at room 
temperature (68° F.) has a viscosity of 2.3 centi- 
poises and at 30° Brix only 3.2 centipoises. 
However, as the concentration of the sugar 
increases, the viscosity increases at an ex- 
tremely rapid rate. Thus, to treble the sugar 
concentration from 20° to 60° Brix increases the 
viscosity from 2.3 to 44 centipoises — more than 
a nineteenfold increase. 

The change in viscosity is even more pro- 
nounced in sucrose solutions with densities in 
the range of standard sirup (66.0° Brix). 

As shown in the table, the viscosity of sirup 
at room temperature (68° F.) is lowered 34.8 
centipoises if its density is 1° Brix below stand- 
ard density. It is lowered 61.9 centipoises if it is 
2° Brix below standard density. The lowered 
viscosity has a marked adverse effect on the 
keeping quality of the sirup and on its accept- 
ance by consumers. The tongue is extremely 
sensitive to these differences. 

The tongue is also sensitive to slight in- 
creases in the density of sirup above 66.0° Brix 
at room temperature. An increase of only 1° 
Brix above standard density increases the vis- 
cosity of sirup 45.8 centipoises; and the sirup 
acquires a thick, pleasant feel to the tongue. 



72 



AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE 



Table 12. — Boiling temperature above that for 
water for solutions of different concentrations 
of sugar 



Temperature 
elevation, ° F 


Sugar 
solutions 


Temperature 
elevation, ° F. 


Sugar 

.solutions 


0.0 


Percent 
0.0 
7.5 

13.8 

19.0 

23.4 

27.1 
30.3 
33.4 
36.0 
38.4 

40.5 
42.5 
44.3 
46.0 

47.7 

49.0 
50.4 
51.6 
52.8 
53.9 

54.9 
55.9 
56.9 

57.8 
58.8 


5.0 
5.2 
5.5 
5.6 
5.8 

5.9 . 
6.1 . 

6.4 . 
6.6 . 
6.9 . 

7.1 . 
7.3 . 

7.5 . 

8.0 . 

8.2 . 

8.5 . 

8.8 . 

9.1 _ 
9.5 _ 

9.9 _ 

10.4 _ 
10.7 . 
11.1 _ 

11.5 _ 

12.0 _ 




Percent 
59.7 


0.2 


^^ 


60 4 


0.4 




61.5 


0.6 




62 


0.8 




62.5 


1.0 




62 9 


1.2 




63.4 


1.4 




64.4 


1.6 




64 9 


1.8 




65 6 


2.0 




66 


2.2 




66.5 


2.4 




67 


2.6 




68 


2.8 


68 5 


3.0 


69 


3.2 


69 5 


3.4 




70 


3.6 




70.5 


3.8 




71 


4.0 




71.6 


4.2 




72 1 


4.4 




72.5 


4.6 




73 


4.8 




73 5 









Thus, the thicker the sirup, the better it tastes. 
However, sirup with a density of more than 67° 
Brix crystallizes on storage at room tempera- 
ture; 67° Brix, therefore, becomes the upper 
permissible density. 

EfTect orTemiMM-atiiiT on N iscosily 

As the temperature of a sugar solution in- 
creases, its viscosity drops sharply. Standard- 
density sirup at its boiling point has a viscosity 
of about 6 centipoises, which is only one.thir- 
tieth that of sirup at room temperature; that is 
why sirup filters so much better when it is at or 
near its boiling point. Likewise, the viscosity of 
boiling sirup with a density between 50° and 60° 
Brix is approximately one-half that of stand- 
ard-density sirup; and that is why it is advanta- 



geous to filter sirup just before it is transferred 
to a finishing pan, when its density is approxi- 
mately 60° Brix or less. 

This lowering of the density by heating sirup 
explains why hot sirup, even though it is of 
standard density, tastes thin and watery. 

Old Stan(iar<l»; <)f FinLshed .Sirup 

In the past, the finishing point of sirup was 
determined by a number of methods. None of 
these methods was precise, and their skillful 
use was an art. For that reason, comparatively 
few men won the enviable title of "sugar- 
maker." 

Typical of these methods was the "blow" test. 
In this test, a small loop of wire was dipped into 
the boiling sap. When the film that formed 
across the loop required a certain puff of breath 
to blow it off, the sirup was considered finished. 
Another method more commonly used was the 
"apron" test. In this test, a scoop was dipped 
into the boiling sap and then held in an upright 
position to drain. Formation of a large, thin 
sheet or apron with the right shajDe and other 
characteristics indicated that the sirup was 
finished. 

L M- ol' \*vvvisiou lii.sti-iini('iil!< 

Precision instruments are now available by 
which the finishing point of sirup can be deter- 
mined easily and with a high degi-ee of accu- 
racy. As concentration progresses, there is a 
progressive increase in the boiling point, in 
density, and in refractive index. These can be 
measured accurately and precisely with a ther- 
mometer, a hydrometer, and a refractometer, 
respectively. However, only the elevation of the 
boiling point is applicable to a sugar-water 
solution, such as sap, while it is actively boiling. 

Kl^'^alion ol' B4Mliii<>: I'oinI 

Chart 15 and table 12 show the changes in 
boiling-point temperature for sugar solutions at 
different concentrations. When a sugar solution 
has been evaporated to the concentration of 
standard-density sirup (66.0° percent of sugar, 
or 66.0° Brix), its boiling point has been ele- 
vated 7.1° F. above the boiling point of water. 
Between 0° and 2T Brix, there is only a slight 



MAPLE SIRUP PRODUCERS MANUAL 



73 




20 40 60 
SUCROSE CONCENTRATION (PERCENT) 

Chart 15. — Curve showing the relation between the con- 
centration of a sugar solution (sap) and the elevation of 
its boiling point above the boiling point of water. 

elevation in boiling point. However, as the solu- 
tion neai's the concentration of standard-den- 
sity sirup, a change of only 2.5 percent in sugar 
concentration (from 64.5° to 67° Brix) raises the 
boiling point 1°. Hence, the boiling point method 
of measuring sugar concentrations is ideally 
suited to sirupmaking. 

Any Fahrenheit thermometer calibrated in 
degree or half-degree intervals and with a 
range that includes 225° F. can be used. For 
greatest usefulness and accuracy, the distances 
between degree lines should be as open as 
possible and should be calibrated in one-fourth 
degrees. 

Elevation of the boiling point as used hei'e 
means the increase in temperature (° F.) of the 
boiling point of the sugar solution above the 
temperature of boiling pure water. It has noth- 
ing to do with the specific temperatui'e 212° F. 
except when the barometric pressure is 760 
millimeters of merciu'v. Under actual condi- 



tions of sirupmaking, the barometric pressure 
is seldom at 760 millimeters; therefore, it is best 
not to associate the fixed value of 212° F. with 
the boiling point of water. 

The recommended procedure is to establish 
the temperature of boiling water on the day 
and at the place sirup is being made. To do this, 
merely heat water to boiling, insert the bulb of 
a liquid stem thermometer or the stem of a dial 
thermometer, and note the temperature while 
the water is actually boiling. This is the true 
temperature of boiling water for the barometric 
pressure at that time and place. In practice, the 
boiling sap in the sap pan can be used to 
establish the temperature of boiling water 
since, as was shown in chart 15, at low-solids 
concentrations (up to 10° BrLx) there is little 
elevation of the boiling point. The boiling tem- 
perature of standard-density sirup is then 
found by adding 7° to the temperature of the 
boiling sap. 

It is of the greatest importance to redeter- 
mine the temperature of boiling water (sap) at 
least once and preferably several times each 
day, especially if the barometer is changing. A 
change in the weather usually indicates a 
change in barometric pressure. The result of 
failure to making frequent checks on the boiling 
point of water is illustrated in the following 
examples: 

On March 1, at Gouverneur, N.Y., the boiling 
point of water was determined to be 210° F., 
which established the boiling point of standard- 
density sirup as 217°. On March 2, the producer 
neglected to redetermine the boiling point of 
water, assuming it to be unchanged, and con- 
tinued to use 217" as the boiling point of sirup. 
Actually, the barometric pressure had fallen, 
which lowered the boiling point of water to 208° 
and of standard-density sirup to 215°. The sir- 
upmaker, by using the temperature of 217°, 
was boiling his sirup 2° too high, and the sirup 
contained 69.8 percent of solids instead of 65.8 
percent (table 12). This high-density sirup re- 
sulted in the production of fewer gallons of 
sirup; and, in addition, the sirup crystallized in 
storage, since it was above 67° Brix. 

If, on the other hand, the reverse had oc- 
curred, the sirupmaker would have made sirup 
with a boiling point 2° F. too low. This sirup 
would contain only 59.7 percent of solids as 



74 



AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE 



Table 13. — Viscosity of sucrose solutions of various densities (° Brix) at temperatures of 20° C. (68° 

F.)tol05° C. {221° F.y 



I 


Density 
solution 
;° Brix) 










Viscosity (centipoises) at — 










of 

( 


20° C. 
(68° F.) 


30° C. 

(86° F.) 


40PC. 
(104; F.) 


50° C. 
(122° F.) 


60° C. 
(140° F.) 


70° C. 80° C. 
(158° F.) (176° F.) 


90° C.2 
(194° F.) 


100° C- 103.5° C.2 105° C.= 
(212° F.) (218.3° F.) (221° F.) 


20 
30 




2.3 

3.2 

15.3 

44.0 

69.2 

_ 82.4 
. 99.1 
. 120.1 
_ 147.2 

. 182.0 

. 227.8 
. 288.5 
_ 370.1 
. 481.6 


1.5 

2.4 

10.1 

33.8 

39.3 

46.0 
54.3 
64.5 

77.3 

93.5 

114.1 
140.7 
175.6 
221.6 


^1.2 

1.8 

7.0 

21.0 

24.1 

27.8 
32.3 
37.7 
44.4 

52.6 

62.9 

76.0 

92.6 

114.0 


1.0 

1.5 

5.0 

14.0 

15.8 

17.9 
20.5 
23.7 

27.5 

32.1 

37.7 
44.7 
53.3 
64.4 


0.8 
1.2 
3.8 
9.7 
10.9 

12.2 

13.8 
15.7 
17.9 

20.6 

19.4 
22.6 
26.3 
31.0 


0.7 
1.0 
2.9 
7.0 
7.6 

8.6 

9.7 

10.9 

12.4 

14.1 

16.1 

18.4 
21.4 
25.0 


0.6 
.9 
2.3 
5.2 
5.7 

6.4 
7.1 
7.9 
8.8 

9.9 

11.3 
12.8 
14.7 
16.8 


















50 
60 
61 

62 
63 
64 
65 

66 

67 


1.8 
4.4 
4.7 

5.0 
5.6 
6.3 
7.0 

7.8 


1.6 
3.6 
3.8 

4.1 
4.6 
5.1 

5.8 

6.6 


1.5 
3.4 
3.6 

3.9 
4.3 
4.8 
5.4 

6.2 


1.5 
3.4 
3.5 

3.8 
4.2 
4.7 
5.3 

6.1 


68 










69 












70 





















' Based on data from Circular C440 issued by the National Bureau of Standards, U.S. Department of Commerce, July 
31. 1958. 

' Values obtained by extrapolation. 



sugar. It would not meet specifications for 
standard-density sirup, would tend to spoil eas- 
ily, and would have a low viscosity and there- 
fore would taste watery. 

Therefore, with a good indicator to detect the 
end point of evaporation (thermometer cali- 
brated in V4° F.), together with the slowdown in 
rate of evaporation, as shown in chart 16, the 
sirupmaker is able to stop evaporation precisely 
at the desired concentration. He can do this 
either by drawing off the sirup from the evapo- 
rator or, if he uses a finishing pan, by turning 
off the heat. 

Finishing Pan 

When a finishing pan is used, it is necessary 
to know when the sap has been concentrated 
enough to be transferred from the evaporator 
to the finishing pan. This can be determined by 
measuring the elevation of the boiling point of 
the partly concentrated sap. Table 12 shows the 
elevation of the boiling temperature of sugar 
solutions (above that for water) for concentra- 
tions from 0° to 73.5° Brix. 

To use the table, determine the boiling tem- 
perature of pure water and then observe the 



boiling temperature of the partly evaporated 
sap. The difference between the two boiling 
points represents the elevation in boiling tem- 
perature. 

Two examples of how to select a boiling point 
elevation to give sirup of a desired density 
(° Brix) follow: 

Example 1. A producer wants to draw off 
sirup from the evaporator at about 40° Brix. At 
what boiling temperature should the sirup be 
removed if water boils at 210° F.? 

Table 12 shows that the boiling temperature 
is elevated 2.0° F. for solutions having a density 
of 40.5° Brix. Thus, when the boiling tempera- 
ture rises to 212° F. (210° + 2°), the sap will be 
concentrated to approximately 40° Brix. 

Example 2. A producer wants to concentrate 
the sap to 50° Brix in the evaporator before 
transferring it to the finishing pan. At what 
boiling temperature should the sirup be drawn 
off if water boils at 211.5° F.? 

Table 12 shows that for solutions having a 
density of 50.4° Brix, the boiling temperature is 
3.2° F. above the boiling point of water. Thus, 
211.5° + 3.2°, or 214.7°, is the boiling tempera- 
ture of 50° Brix sirup. 



MAPLE SIRUP PRODUCERS MANUAL 



75 




20 30 40 50 

BRIX (DEGREES) 



Chart 16. — Change in the rate of loss of water by evapora- 
tion, with constant heat, as the concentration of sap 
increases. Boiling sap with an initial density of 22° Brix 
loses 42 grams of water per minute, whereas sirup with 
a density of 65° loses only 15 grams of water per 
minute, a threefold decrease in rate. 

Special Theniionietei*s 

In sirupmaking, a knowledge of the boiling 
point of standard-density sirup in ° F. is impor- 
tant provided a temperature reference point 
(the boiling point of water) is established and 
the correct boiling point of sirup is located 7 
above it. On this basis, special thermometei's 
have been developed for use in making sirup: 
The liquid-stem thermometer with movable tar- 
get, the liquid-stem industrial thermometer, 
and the dial thermometer with movable dial. 

Target Tlierntonieter 

The target thermometer does not have any 
markings on the stem. The degree lines on a 
movable target refer to the boiling point of 
water rather than to ° F., as on the conven- 
tional Fahrenheit thermometei-. 

The target thermometer is calibrated by plac- 
ing the bulb in either boiling water or boiling 
sap. The target is moved by means of an adjust- 
ing screw until the line "water boils" coincides 
with the top of the mercury column. The line 
"sirup" is exactly 7° above the line "water 
boils." This is the boiling point of standard- 
density sirup for that hour and place. After 
adjustment, the thermometer is placed in the 
sirup pan adjacent to the place where the 
sirup is drawn off. 



Unfortunately, any thermometer set in the 
evaporator will be surrounded by steam, which 
makes it difficult to read (fig. 91). 

Use of a flashlight' to illuminate the ther- 
mometer and a large funnel to divert the steam 
makes viewing easier. The funnel is held with 
the tip toward the thermometer, and the ther- 
mometer is viewed through the funnel with the 
aid of the flashlight. 

Liqiiitl-Slrm Inthistrial Thcriiiomflfr 

The liquid-stem industrial thermometer does 
not have special markings or a movable target. 
But it does have an open scale — a lineal dis- 
tance of approximately 3 inches for 10° F., 
which is almost three times that of other ther- 
mometers (fig. 92). It is calibrated in hU" and has 
a magnifying device. These features make it 
ideal for use in sirupmaking. These thermome- 




PN-4787 

Figure 91.— The target thermometer is placed in the 
boiling sirup. The fine mercury column is difficult to 
see because of the steam. The boiling sirup being tested 
must be deep enough to cover the bulb of the thermom- 
eter. The thermometer must be in boiling sirup and as 
close to the point of sirup drawoff as possible. 



76 



AGRICULTURE HANDBOOK i:{4, U.S. DEPT. OF AGRICULTURE 




PN-4788 

Figure 92. — The liquid-stem industrial thermometer has 
an open scale that permits calibration marks for each 
''4° F. and the temperature of the boiling sirup can be 
measured precisely. The thermometer is mounted out- 
side the pan so it is not obscured by steam. It is 
especially suited when the pan is covered with a tight 
steam hood. 



ters can be obtained with the stem bent at 
right angles and protected with metal armor. 

The right-angle thermometer is mounted 
through the wall of the sirup or finishing pan 
using a special fitting. This arrangement per- 
mits the thermometer to be mounted high 
enough on the sidewall of the evaporator or 
finishing pan to be above the level of the sirup 
so that the thermometer can be removed for 
cleaning without loss of sirup. It also locates 
the scale of the thermometer at an obtuse 
angle for easy reading. 

The thermometer is calibrated each day in 
terms of the boiling point of water. The bulb is 
immersed in water, the water is brought to a 
boil, and the temperature is noted. To this 
observed temperature is added 7°, the tempera- 
ture elevation required to give the boiling point 
of standard-density sirup (see table 12). 



Dial Thermomt'tt'r 

The degi'ee lines of the dial thermometer (25), 
like the target thermometer, refer to the boiling 
point of water (fig. 93). This thermometer has a 
bimetallic element in the first 3 or 4 inches of 
the stem. As the indicator is a needle, the 
openness of scale is governed by the length of 
the needle and the accuracy required. The scale 
is twice as open in a dial thermometer 5 inches 
in diameter as in the target thermometer. 

The dial thermometer is calibrated by im- 
mersing the part of its stem that contains the 
bimetallic element in boiling water or sap the 
same distance that it is immersed in the sirup; 
when the indicating needle comes to rest, the 
dial is rotated by means of an adjusting screw 
until the zero or water boils line coincides with 
the pointer. Then the sirup line is located T F. 
above the zero or water boils line to indicate 
the boiling temperature of standard-density 
sirup for that day and place. 

The long straight stem of this thermometer is 
inserted through the wall of the sirup pan and 
sirup drawoff box so it will be parallel to the 
bottom of the pan and entirely immersed in the 
boiling sirup. The dial of the thermometer is on 
the outside of the evaporator where it is out of 
the steam and is easy to read (fig. 93). 



Hydixjnietei'S 

A hydrometer is not the ideal instrument for 
judging the finishing point of sirup. It is not 
calibrated for use at the temperature of boiling 
sirup, and it cannot be used to follow the 
concentration of the sap continuously. For ac- 
curacy, the exact temperature of the sirup 
being tested with the hydrometer must be 
known so that the necessary corrections can be 
made. However, the hydrometer and refractom- 
eter are the only instruments that can be used 
to measure the density of sirup that is not in an 
actively boiling state. 



•Hot Test' 

The "hot test" is often used to determine 
whether the process of evaporating sap to sirup 
is completed. It is made as follows: 



MAPLE SIRUP PRODUCERS MANUAL 



77 




PN-4789 

Figure 93. — The dial thermometer, like the tai'get ther- 
mometer, has markings to indicate O, water boils, 
sirup, soft tub, and cake sugar. The dial thermometer, 
like the industrial thermometer, is mounted on the 
outside of the evaporator. 



PN-4790 

Figure 94. — Sirup at approximately 210° F. is used in 
making the hot test. The hydrometer cup is raised to 
eye level and the reading is made as soon as the 
hydrometer comes to rest. 



Fill the hydrometer cup with boiling sirup 
from the evaporator or finishing pan (fig. 94). 
Immediately place the hydrometer in the sirup 
and, as soon as the hydrometer comes to rest, 
make the observed density reading. Perform all 
operations as quickly as possible. If the ob- 
served hydrometer reading is between 59.3° and 
59.6° Brix, the evaporation of the sap to stand- 
ard-density sirup is completed. 

For best results with the hot test, the tem- 
perature of the hot sirup must be between 210° 
and 218" F. at the moment the hydrometer 
reading is made. To be sure that the sirup is in 
this temperature range, first determine the 
temperature of the hot sirup as follows: 

Fill the hydrometer cup with boiling sirup. 
Place the hydrometer and the thermometer in 
the sirup. Then, instead of i-eading the hydrom- 
eter, measure the temperature as soon as the 
hydrometer comes to rest. Repeat this proce- 
dure and, if the two consecutive temperature 



readings are not obtained in the range of 210° 
to 218' F., speed up the operation until these 
temperatures are obtained at the time hydrom- 
eter readings are made. 

The hot test is not a precise measurement. It 
is extremely difficult to make accurate hydrom- 
eter and temperature readings at the same 
time in sirup that is hotter than 180° F. because 
the sirup is cooling rapidly. 

Fi-om the time the hydrometer cup is filled 
with boiling sirup until the observed hydrome- 
ter reading is made, the sirup will have cooled 
several degi-ees. The amount of cooling depends 
on the time involved and the temperature of 
the air surroimding the hydrometer cup. 

Hydrothcrin 

The hydrotherm, a special hydrometer (chart 
17), has a liquid thermometer built into it that 
automatically locates the point on the hydrome- 
ter (top of thermometer liquid column) for 



78 



AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE 



measuring standard-density sirup. The accu- 
racy of this instrument depends on the relation 
of Uneal expansion of the thermometer Hquid to 
Hneal displacement of the hydrometer stem by 
standard-density sirup at different tempera- 
tures. When used, sufficient time must be al- 
lowed for the thermometer of the hydrotherm 
to warm or cool to the temperature of the sirup, 
usually about 30 to 40 seconds. 

Since the hydrotherm is not calibrated, the 
scale does not indicate how much too dense or 
too thin the sirup is. 

Suinmarv 

(1) Finished sirup must contain not less than 
66.0 percent of solids (66.0" Brix) at a tem- 
perature of 68° F. 

(2) Table sirup that is between 66° and 67° Brix 
has the best taste. Table sirup that is below 
standard density tastes thin. 

(3) Use precision instruments to measure 
standard-density sirup. 

(4) The boiling temperature of standard-den- 
sity sirup is T F. above the temperature of 
boiling water. 

(.5) Use a thermometer calibrated in V4° F. to 
measure the temperature of boiling sirup. 

(6) Calibrate the thermometer frequently with 
reference to the boiling point of water. 

(7) Completely immerse in the boiling water or 
sap the bulb of the stem of a liquid ther- 
mometer or that part of the stem of a dial 
thermometer containing the bimetallic ele- 
ment. 

(8) To test hot sirup with a hydrometer, the 
temperature of the sirup must be noted and 
necessary temperature corrections applied 
to the observed hydrometer readings. Hot 
sirup (210° to 218' F.) of standard density is 
59. y to 59.6° Brix. 

(9) To test hot sirup with a hydrotherm, suffi- 
cient time must be allowed for the hydro- 
therm to come to the same temperature as 
the sirup in which it is floated. 



STANDARD 

DENSITY 

SIRUP 




THERMOMETER 




Chart 17. — Hydrotherm for measuring density of sirup. It 
automatically compensates for temperature correction. 



(;L\RIFK:ATlo^ ok SIRl I' 



Snjjar Sainl 

SirQp as it is drawn from the evaporator 
contains suspended solids, commonly known as 



sugar sand. They are primarily the calcium and 
magnesium salts of malic acid. These salts are 
precipitated because they become less soluble 



MAPLE SIRUP PRODUCERS MANUAL 



79 



as the temperature of the sirup solution in- 
creases and as its concentration increases. 
Sugar sand occurs in various forms, ranging 
from an amorphous black, oily substance to a 
fine, white, crystalline material. Dark sugar 
sand will usually cause the sirup to appear a 
grade or two darker than normal, whereas 
white sugar sand will often cause it to appear 
lighter. 

The amount of this precipitate in the sirup is 
not always the same. Sap from the same sugar 
grove varies from year to year and even within 
the same season. 

Studies at the Ohio (Wooster) Agricultural 
Experiment Station' indicate that trees at high 
elevations tend to produce more sugar sand 
than do those at lower elevations. The Ohio 
workers were not able to show any relation 
between climatological data or soil types and 
amounts of sugar sand formed. 

Sirup to be sold for table use must be clear 
(free of suspended matter) to meet Federal and 
some State specifications. Sirup can be clarified 
by sedimention, filtration, or centrifugation. On 
the farm, sedimentation and filtration are the 
methods generally used. 

Sediiiieiitatioii 

Sedimentation or settling is the simplest 
method of clarifying maple sirup, but it has 
several disadvantages. It cannot be used to 
clarify all sirup. Some sirup contains suspended 
particles so fine that they resist settling. Clari- 
fication by sedimentation requires a long 
time — days and sometimes weeks. After set- 
tling at room temperature, the sirup must be 
reheated to 180" F. before packaging to insure a 
sterile pack. This reheating may darken the 
sirup enough to lower its grade. 

To clarify by sedimentation, the hot sirup is 
first put through a coarse filter, such as several 
layers of flannel or cheesecloth, to screen out 
large particles of foreign matter. It is then 
transferred to the settling tank. The tank 
should be of noncorrosive metal, and its height 
should be at least twice its diameter. It should 
have a dustproof cover and a spigot or other 
means of drawing off the sirup about 2 inches 
above the bottom of the tank. The sirup should 



Unpublished data. 



be left in the tank until samples that are 
withdrawn show it to be sparkling clear. It is 
then drawn from the tank, standardized for 
density, heated to 180° F., and packaged. Sirup 
that has failed to clarify after several weeks of 
standing must be filtered. Because of the un- 
certainty of the sedimentation method, it is 
rapidly losing favor. 

In large operations, the sirup can be kept 
sterile if it is added to the settling tank while it 
is hot (above 180° F.) and if the entire surface of 
the sirup is continuously irradiated by germici- 
dal lamps. 

Filtration 

Filtration of maple sirup is not a simple 
procedure. As with sedimentation, the success 
and ease of clarifying sirup by filtration depend 
on the nature of the suspended particles that 
are to be removed. It is best to use two filters — 
a prefilter to remove the coarse material and a 
thicker filter to remove the fme. In the past, 
the most commonly used prefilter was several 
layers of cheesecloth, outing flannel, or similar 
cloth. Today, a nonwoven rayon material called 
miracle cloth or maple prefilter paper is used 
with considerable success. After prefiltering, 
the sirup is run through a thicker filter. For- 
merly these filters were made of wool, but now 
they usually are a layer of synthetic felt (Or- 
ion). 

Synthetic felt filters have many advantages 
over wool felt filters. They do not impart a 
foreign flavor to the sirup, shrink very little or 
not at all, do not pill, resist abrasion, stain only 
slightly, and have a long life. Synthetic filters 
that have been in use more than 5 years show 
little evidence of wear. 

The disadvantage of the two-filter system is 
that the large particles are removed on the 
coarse prefilter. The fme particles are collected 
on the finishing filter, and they may form a 
compact bed that resists flow of the thick sirup. 

The most common filtration assembly in the 
past was a large milk can in which was inserted 
a cone-shaped, felt bag supported at the top of 
the can. However, this is little used today. 

Hat Filters 

A flat filter consists of a felt sheet for a 
filtering surface (fig. 95) instead of a cone. It 



80 



AGRICULTURE HANDBOOK 134, U.S. DEFT. OF AGRICULTURE 




SUGGESTED FILTER TRAYS 
HEAVY GAGE METAL OR WOOD 



PN^791 

Figure 95. — A simple type of flat filter. A basket of 
hardware cloth is supported above the two tanks for 
holding the felt and above this is the support for the 
prefilter. The prefilter is moved across the tray as new 
filtering surface is needed. 

was first used in New York and is gaining in 
popularity everywhere. The flat filter provides 
a larger filtering area than does the cone- 
shaped filter. Distribution of the filter cake over 
this larger area results in a thiner layer, so the 
filters can be used for longer periods before 
cleaning is necessary. 

The felt sheet is supported in a shallow bas- 
ket of hardware cloth with 2-inch walls {147). 
The felt is cut at least 4 inches larger than the 
bottom of the basket, and the edges are turned 
up 2 inches to form a shallow tray (chart 18). 
Usually the felt can be used two or three times 
longer between cleanings if the sirup is first put 
through a prefilter. However, because of the 
physical form of the particles of sugar sand, 
filtering may be more rapid if the prefilter is 
not used. This can be determined only by exper- 
iment. The prefilter is mounted above the felt 
and is supported on a wire screen basket the 
same size as that used for the felt (chart 18). 
The prefilter is cut to fit across the basket, but 
a length of filter paper is left hanging over the 
edge of the basket. As the prefilter becomes 
clogged, a new filtering surface is provided by 
pulling the prefilter across the basket (fig. 95). 

The filters can be built in multiples over a 
common tank (fig. 96). As one becomes clogged 
with sugar sand, the assembly can be moved to 
place a clean filter under the spigot. 



FELT FILTER 




Chart 18. — Sirup filter. A flat felt filter assembly, con- 
structed on a milk-can washer that serves as a tempo- 
rary storage tank from which the hot sirup can be 
drawn for packaging. Shortening the legs and attach- 
ing casters or wheels permits the assembly to be moved 
easily into place under the sirup drawoff spigot. 

To maintain filtration at a rapid rate the flat 
prefilters and felts must be cleaned often, espe- 
cially if the sirup contains a large amount of 
sugar sand. To clean the filters, the filter cake 
is first scraped off with a wooden scraper to 
prevent damage to the filtere. The entrapped 
sirup is dissolved by dipping the filter into a 
pan of hot water. The filters are folded with the 
sugar sand on the inside so that it will not be 




PX-47y2 

Figure 96. — A more elaborate type of installation in 
which three felt filter units are installed over a com- 
mon tank. The units are mounted on rollers so that 
they can be replaced by a fresh unit when necessan,-. 
The tank is provided with a drawoff valve. 



MAPLE SIRUP PRODUCERS MANUAL 



81 



washed into the recovered sirup. The felt is 
rinsed repeatedly in hot water. The recovered 
sirup is returned to the evaporator. 

A homemade washer for flat filters is shown 
in figure 97. By means of an eccentric, the felt 
is lifted from the hot water and then dunked 
repeatedly for 15 to 30 minutes until it is clean. 
No detergent can be used since it would impart 
an undesirable flavor to the filter. The felts are 
then hung on racks to dry or drain. Two or 
three extra felts are required for replacements 
while the others are being washed. With an 
efficient washing machine, the felts can be 
reconditioned for use so easily that some pro- 
ducers have discontinued using prefilters. 

Filtering: Sfiiiiconcenlrtitcd Siriif} 

When a finishing pan is used, another filter- 
ing procedure has proved very successful. This 
procedure takes advantage of these facts: (1) 
Most of the sugar sand is precipitated (formed) 
and in suspension when the sap is concentrated 
to 55° to 60° BrLx, and (2) hot sap at 55° to 60° 




PN-4793 

Figure 97. — A simple type of machine washes flat filters 
by repeatedly dipping the felts into hot water. 



Brix has a viscosity of only 1..5° centipoises as 
compared to 5.4° for standard-density sirup. 
Therefore, when sap has been concentrated to 
55° to 60° Brix, it is filtered as it is being 
removed from the evaporator and before it is 
transferred to the finishing pan. In bringing 
the sirup to standard density in the finishing 
pan, a small amount of additional sugar sand 
(precipitate) may be formed. This is easily re- 
moved by using another felt filter assembly. 

This final filtration, like all other open filters, 
permits loss of water as steam that escapes 
from the hot sirup. This may increase the 
density of the finished, filtered sirup by as 
much as 1° Brix. To avoid this, a number of 
producei-s pump the sirup from the finishing 
pan through a pipeline to the closed bottling or 
canning tank. Since this is a closed system, 
there is no change in the density of the sirup as 
a result of evaporation. To provide for the final 
or polishing filtration, an inline, cartridge-type 
filter is mounted in the pipeline from the finish- 
ing pan to the holding tank. Two cartridge 
filters are used, mounted in parallel with sepa- 
rate control valves so that they can be used 
alternately. This permits replacing a clogged 
filter without inteiTupting the sirup finishing 
and filtering operation. 



Suiiiinai'v 

Sedinientdtiott 

(1) Strain the sirup through a paper prefilter or 
cheesecloth. 

(2) Place the sirup in settling tanks. 

(3) Allow it to stand until all suspended matter 
has settled out. (Test by periodically draw- 
ing a small sample from the tank spigot.) 

(4) Sedimentation is complete when the sirup is 
ciystal clear as it is drawn off. 

(5) If the sirup is still cloudy at the end of 
several weeks, it can be clarified only by 
filtration. 

Filtration {Preferred Method) 

(1) Run the hot, standard-density sirup from 
the evaporator or finishing tank directly on 
the filters. 

(2) Use flat (preferably) filters consisting of a 
prefilter (paper or flannel) above the felt 
filter. 



82 



AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE 



(3) Change the pre filter and the felt filter as 
often as necessai-y to maintain a rapid rate 
of filtration. 

(4) When using a finishing pan, filter the partly 
evaporated sirup before transferring it to 
the pan. 



(5) If a precipitate forms while the sirup is 
heating in the finishing pan, the sirup must 
be given a final or polishing filter. 

(6) Use a closed system in transferring the 
finished sirup to the holding tank and use 
an inline, cartridge-type filter for polishing 
the sirup. 



CHECKJING AND ADJUSTING DENSITY OF SIRUP 



The one specification that all gi-ades of table 
sirup must meet, irrespective of color or other 
considerations, is density. The minimum allow- 
able density of maple sirup is 66 percent by 
weight of soluble solids (66.0° Brix or 35.6° 
Baume)*' {130a). This corresponds to 11.025 
pounds per gallon of 231 cubic inches at 68° F. 

The density of sirup can be measured in 
three ways: (1) By weight; (2) by refractometry; 
and (3) by hydrometry. 

Vi <Mght Method 

Determining the density of sirup by the 
weight per unit of volume is not recommended 
as a testing procedure for farm use. This test 
can be made only under- the most exacting 
conditions and with precision instruments. The 
gallon measure must have a capacity oi exactly 
231 cubic inches, the temperature of the sirup 
must be exactly 68° F., and the weight of the 
sirup must be determined accurately to within 
0.01 pound. If any one of these conditions is in 
error, the measurement is valueless. For exam- 
ple, an exact gallon of 231 cubic inches of sirup 
at 68^ F. with a Brix value of 63.5° weighs 10.90 
pounds {107), whereas the same volume of sirup 
at the same temperature but with a Brix value 
of 67.5° weighs 11.10 pounds. Thus, two sirups 
could differ 4 percent in their solids content and 
yet differ only 0.2 pound in weight (an amount 
not detected by ordinary scales) so they would 
both appear to weigh 11 pounds per gallon. Or 
an error in weighing of 0.02 pound would cause 
an error in the solids content of approximately 
V2 percent (0.5° Brix). For these reasons, the 
fact that a gallon of minimum density sirup 
weighs 11 pounds does not mean that this is a 



" Bureau of Standards Baunie scale for sugar solutions, 
modulus 14.5. 



recommended criterion for measuring the den- 
sity of sirup. However, it is of great value when 
used properly and should be used to measure 
the amount of sirup sold as 1 gallon. 

Since sirup is packed hot in cans that are 
large enough to allow for the expanded volume 
of the hot sirup, and since all sirup is not 
packaged at exactly the same hot temperature, 
the volume of a gallon of hot, standard-density 
sirup varies slightly. However, a gallon of 
standard-density sirup weighs 11 pounds 
whether it is hot or cold. It is therefore recom- 
mended that all packaged sirup be weighed 
before it is sold to determine if the required 
amount of sirup is in the package — 11 pounds 
for 1 gallon; 2 pounds, 12 ounces for 1 quart; 
and 1 pound, 6 ounces for 1 pint. These are net 
weights and do not include the weight of the 
can or package. 

Refractometrj' Method 

Determining the density of sirup by measur- 
ing its refractive index, which changes in a 
regular manner with changes in the amount of 
dissolved solids, is the simplest of the three 
methods. This method is not generally used 
because it requires a refractometer, an expen- 
sive optical instrument (fig. 98). However, the 
precision with which density can be measured 
with the refractometer makes it well suited for 
use by Federal and State inspection services, by 
judges of sirups in competition, and by central 
evaporator plants. This instrument is not satis- 
factory for measuring the density of hot sirup 
(180° F. and above). 

H.vdi-oineti-> Method 

Hydrometry is the most generally used 
method for measuring the density of cold sirup, ' 



MAPLE SIRUP PRODUCERS MANUAL 



83 




PN-4794 

Figure 9S. — Checking the density of sirup with a refrac- 
tometer. Only one drop of sirup is required for this 
measurement. 

and it is best suited for use by the sirupmaker. 
All that is required to make precise density 
measurements is a relatively inexpensive but 
accurate hydrometer, a thermometer, and a 
hydrometer tube or jar (fig. 99). Hydrometry is 
based on the Archimedes principle that the 
density of a liquid can be measured by the 
displacement of a floating body. The hydrome- 
ter, a partly immersed body, displaces a volume 
of liquid having a mass equal to the weight of 
the hydrometer. A hydrometric measurement 
is made by noting the point on the hydrometer 
stem that is in contact with the surface of the 
liquid. The hydrometer must be at rest and 
floating freely in the liquid, as shown in chart 
19. The density value is read from a scale sealed 
in the stem. 

The accuracy of a hydrometer measurement 
depends on the spacing of the markings on the 
scale in the hydrometer stem, which in turn 
depends on the diameter of the stem. Thus, the 
thinner the stem, the farther apart the mark- 
ings, and the greater the accuracy with which 
the density measurements can be made. The 
scale of hydrometers for measuring density of 
sirup may be marked and calibrated in or on 
the stem of the hydrometer (chart 20). These 
scales can be marked by one of three systems or 
a combination of the systems: (1) Specific grav- 
ity; (2) Brix scale; or (3) Baume scale. 



HYD ROMETER STEM 



7^ 



READING 
POINT 



Chart 19. — Hydrometer used for measuring density. The 
hydrometer can should be filled to the top. It should be 
held at eye level for reading. 

Both specific gravity and the Baume scale 
relate the weight of a unit volume of maple 
sirup (the solution being tested) to some other 
liquid used as a standard; they give no direct 
information regarding the solids content of the 
sirup being tested. 

Brix Sfdif 

The Brix scale relates the density of sirup to 
sugar solutions of the same density and known 
percentages of sugar. The Brix value does not 
express the true percentage of sugar in a solu- 
tion containing sugar plus other dissolved sol- 
ids; rather, it indicates what the percentage of 
sugar would be if the density of the solution 
were due only to dissolved sugar. The Brix 
scale is particularly well suited for measuring 
the density of maple sirup because 98 percent of 
the dissolved solids is sugar. For practical pur- 
poses, the Brix value equals the percentage of 
sugar in the sirup. 



84 



AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE 




PN-4796 

Figure 99. — A hydrometer is a simple, inexpensive instru- 
ment for precisely measuring the density (" Brix) of the 
sirup. The hydrometer should be read at eye level. The 
temperature of the sirup must be measured and a 
temperature correction made. 



A good approximation of the weight of sugar 
in any lot of maple sirup, whether or not it is 
standard-density sirup, can be found by multi- 
plying the weight of the sirup by its density 
(° Brix) and dividing by 100. This information is 
important to the producer who sells his sirup 
wholesale, since the price is based on its solids 
(sugar) content. Thus, 100 pounds of sirup at 65° 
Brix contains 65 pounds of sugar, whereas 100 
pounds of standard-density sirup (66.0° Brix) 
contains 66.0 pounds of sugar. Therefore, 100 
pounds of the low-density sirup has a lesser 
value than 100 pounds of standard-density sir- 
up. Likewise, 100 pounds of sirup with a den- 
sity of 66.8° Brix contains 66.8 |X)unds of sugar, 
which is more than that contained in 100 
pounds of standard-density sirUp, and it has a 
greater value. If sirup has an original density 
of more than 67° Brix, the excess sugar will 
precipitate out, and the hydrometer will not 
measure it. 

To obtain the weight of sugar in sirup when 
density is measured by a hydrometer whose 



VT BAUME 

(eo'F) 



25 



HYDROMETERS 



NY BAUME BRIX 
(68°E) 



BRIX 

(ee-E) 



r~\ 



30 



35 






30 



60 
61 
62 

63 
64 
65 
66 
-167 
J 68 



Chart 20. — The three hydrometer scales used in testing 
sirup. Left, Vermont Baume scale, marked for testing 
sirup at 60° F.; standard-density sirup at this tempera- 
ture is indicated by the heavy line at 36°. Center, 
hydrometer with double scale, marked for testing sirup 
at 68°; standard-density sirup on the Baume scale of 
this hydrometer is indicated by the hea\y line at 35.27°. 
The double scale requires a spindle so large in diameter 
that accurate readings are difficult to make, since the 
scale must be compressed, ffi^/if, Brix scale, marked for 
testing sirup at 68°; standard-density sirup at this 
temperature is indicated by the heavy line at 65.46°. 

scale is in specific gi-avity or ° Baume requii-es 
more involved calculation because neither scale 
has a direct relation to the amount of sugar 
present. 

Baume Scale 

Even though the Baume scale does not ex- 
press directly the solids content of maple sirup 
and its continued use cannot be recommended, 
its long past use by the maple industry justifies 
the following explanation and the tabulation on 
page 85 for the conversion of Baume values 
(points) to ° Brix. 

The Baunie scale relates the density of a 
liquid to that of a salt solution, but it is more 



MAPLE SIRUP PRODUCERS MANUAL 



85 



convenient to calculate the Baume value from 
specific-gravity tables. Thus, " Baume = sp. g. 
(sp. g.) 



(M) 



, where M = the modulus. 



In the past, unfortunately, neither the tem- 
perature for which the Baume scale was cali- 
brated nor M was standardized. Today, M is 
standardized at 145. The temperature for cali- 
bration is standardized at 68° F. (except in Ver- 
mont). In Vermont, the scale is marked at 36° 
(for use at 60° F.), and standard-density sirup 
has a Baume reading of 36° when measured at 
60° F. In other States and for Federal sjjecifica- 
tions, the scale is marked at 35.6° (for use at 
68° F.). When this scale is used, standard-den- 
sity sirup has a Baume reading of 35.6° at 68°. 
When a Baume hydrometer is used, caution 
must be exercised in observing the temperature 
at which the scale is to be used. 

Aleasiirinff Doiisitv 

Measuring the density of sirup by hydrome- 
try is relatively simple. Many people, however, 
incorrectly assume that the observed hydrome- 
ter reading is the true density of the sirup. This 
error occurs because they neglect to consider 
that sirup and sap are water solutions and 
therefore behave as water does, expanding and 
contracting with changes in temperature. 

Most hydrometers and re fracto meters made 
for use in this country are calibrated for use at 
68° F. When used to measure sirup at this 
temperature, the observed hydrometer or re- 
fractometer value of the sirup is the true value. 
If sirup is heated above 68° F., it will expand to 
a greater volume and its apparent (observed) 
density will be less than its true density. Like- 
wise, if sirup is chilled below 68°, it will contract 
to a smaller volume and its apparent (observed) 
density will be gi-eater than its true density and 
corrections must be made. 

To make exact density measurements, sensi- 
tive hydrometers that can be read with high 
precision must be used. The diameter of the 
hydrometer stem, therefore, must be small 
enough so that a change in the density of the 
sap or sirup equivalent to 0.1° Brix will cause 
an observable change in the depth at which the 
hydrometer stem floats, as measured at the 
intersection of the liquid surface and the hy- 



drometer stem. The hydrometer will have a 
scale with 0.1° Brix graduations and will usu- 
ally cover a range of 10° to 12° Brix. The stem 
will be approximately 6V2 inches long, and the 
overall length of the hydrometer will be about 
13 inches. This type of hydrometer will require 
a hydrometer cup at least 13 inches deep. 

Since the Brix scale gives the density of sap 
or sirup directly in terms of dissolved solids as 
percentage of sugar, it is ideally suited for use 
by the maple industry. However, as stated ear- 
lier, many sirup hydrometers in use today have 
Baume scales. Baume values (commonly called 
points) can be converted to Brix values, as 
follows: 



Brix 



Baume 



Bri,\ 



Baume 



Brix 



0.0 0.0 

0.1 .1 

0.2 .1 

0.3 .2 

0.4 .2 

0.5 ..3 

0.6 .3 

0.7 .4 

0.8 .5 

0.9 .5 

1.0 .6 

1.1 .6 

1.2 .7 

1.3 .7 

1.4 .8 

1.5 .8 

1.6 .9 

1.7 1.0 

1.8 1.0 

1.9 1.1 

2.0 1.1 

2.1 1.2 

2.2 1.2 

2.3 1.3 

2.4 1.3 

2.5 1.4 

2.6 1.5 

2.7 1.5 

2.8 1.6 

2.9 1.6 

3.0 1.7 

3.1 1.7 

3.2 1.8 

3.3 1.9 

3.4 1.9 

3.5 2.0 

3.6 2.0 

3.7 2.1 



3.8 2.1 

3.9 2.2 

4.0 2.2 

4.1 2.3 

4.2 2.4 

4.3 2.4 

4.4 2.5 

4.5 2.5 

4.6 2.6 

4.7 2.6 

4.8 2.7 

4.9 2.7 

5.0 2.8 

5.1 2.9 

5.2 2.9 

5.3 3.0 

5.4 3.0 

5.5 3.1 

5.6 3.1 

5.7 3.2 

5.8 3.2 

5.9 .3.3 

6.0 3.4 

6.5 3.6 

7.0 3.9 

7.5 4.2 

8.0 4.5 

8.5 4.7 

9.0 5.0 

9.5 5.3 

10.0 5.6 

10.5 5.9 

11.0 6.1 

11.5 6.4 

12.0 6.7 

12.5 7.0 

13.0 7.2 



Baume 



13.5 7.5 

14.0 7.8 

14.5 8.1 

15.0 8.3 

15.5 8.6 

16.0 8.9 

16.5 9.2 

17.0 9.5 

17.5 9.7 

18.0 10.0 

18.5 10.3 

19.0 10.6 

19.5 10.8 

20.0 11.1 

20.5 11.4 

21.0 11.7 

21.5 11.9 

22.0 12.2 

22.5 12.5 

23.0 12.7 

23.5 13.0 

24.0 13.3 

24.5 13.6 

25.0 13.8 

25.5 14.1 

26.0 14.4 

26.5 14.7 

27.0 14.9 

27.5 15.2 

28.0 15.5 

28.5 15.8 

29.0 16.0 

29.5 16.3 

30.0 16.6 

30.5 16.8 

31.0 17.1 

31.5 17.4 



86 AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE 



Brix ° Baume ° Brix ° Baume " Brix ° Baume 



Measuring Solids (Content 



32.0 17.7 58.0 31.5 64.8 34.9 The effect of temperature on density is more 

32.5 17.9 58.5 31.7 64.9 35.0 pronounced in siruD than in sap {H6). Since 

33.0 18.2 59.0 32.0 . . ■ ' ^u \.u e u 

33.5 18.5 59.5 32.2 65.0 35.0 ^^^"P '^ "'^^^ viscous than sap, the followmg 

34.0 18.7 65.1 _ __ 35.1 precautions should be observed: 

34.5 19.0 gQQ ^2 5 65.2 35.1 No sirup must be allowed on the part of the 

35.0 19.3 gjj J 32.5 -~^^-^ ^^-^ hydrometer stem that is exposed above the 

35.5 19.6 gQ2 32.6 ^^■'^ ^^-^ surface of the sirup being tested. The hydrome- 

60.3 32.6 • • ter must be clean and dry, and it must be 

36 n 19 8 fin 4 "^9 1 oo.b 35. o 

365 ' ' 20 1 qp 7 65.7 35.4 inserted with clean fingers. Also, it must not be 

37.0 V. ... 2QA 606 32 8 ^^-^ ^^-^ submerged below its floating position and per- 

37.5 20.6 60.7 32.9 ^^'^ ^^-^ mitted to rise. The sirup on the exposed stem of 

38.0 20.9 60.8 32.9 the hydrometer would add weight, the hydrom- 

38.5 21.2 60.9 33.0 ^^'^ ^^-^ 

39.0 21.4 



60.9 33.0 • • eter would float too deep in the sirup, and the 



48.5 26.5 

49.0 26.8 



66.1 35.6 



go g 21 7 66.2 __ 35.7 observed reading would be too low. 

4o!o ~ ~- 22^0 ^^'^ ^^'^ 66.3 35.7 Sirup at room temperature is viscous, and 

40.5 22.2 „ ■ „ „■ 66.4 35.8 therefore 30 seconds or more will be required 

61 3 V 33 2 ^^'^ ^^'^ fo^ ^^^ hydrometer to settle to its point of rest. 

41.0 22.5 61.4 33.2 gg",, org If the observed hydrometer readings are made 

41.5 22.8 61.5 33.3 gg'g gg^^ too soon, they will be too high. Also, if the 

42.0 23.0 61.6 33.3 gg g gg q diameter of the hydrometer cup is too small, or 

43 23 6 618 33 4 if the hydrometer is floated too close to the wall 

43.5 23.8 619 ... 33^5 ^'"^ ^^'^ of the cup, or if the cup is tilted, the movement 

44.0 24.1 ^'^■^ 36.1 of i]]Q hydrometer will be restricted and the 

44.5 24.4 g2(, gg g 67.2 36.2 observed reading will be incorrect. 

45.0 24.6 g2^ gg g ^^-^ ^^-^ rpQ determine accurately the sugar content of 

• • 62.2 33.6 67.5 36.3 maple sirup, use a hydrometer calibrated in 0.1° 

4gjj 62.3 33.7 67.6 36.4 Brix (7.46). Place the sirup in a hydrometer cup 

46.5 '/.'".'. 2bA 625 33 8 ^''"^ ^^'^ whose depth is equal to, or slightly greater 

47.0 25.7 62^6 33.8 67 9 365 than, the overall length of the hydrometer and 

47.5 26.0 g2 7 339 ' ' whose diameter is at least IV2 times larger than 

'!?■? ??■? 62.8 33.9 ggQ ggg the diameter of the hydrometer bulb. Fill the 



62.9 34.0 



;.l 36.6 hydrometer cup to the top with sirup, gently set 

495 """"'" 27^^ 68.2 36.7 the hydrometer into the sirup, and allow it to 

50.0 27.3 ^^"^ ^^-^ 68.3 36.7 settle unaided until it comes to rest. When the 

50.5 27.5 f^\ l^-\ 68.4 36.8 hydrometer comes to rest, at least 30 seconds 

63.3 34.2 68.6 36 9 after it IS placed m the cup, carefully hit the 

51.0 27.8 63.4 34.2 68.7 36.9 cup SO that the liquid surface is at eye level and 

51.5 28.1 63.5 34.3 68.8 37.0 read the mark on the hydrometer scale at the 

52.0 28.3 63.6 34.3 68.9 37.0 point of intersection of the hydrometer stem 

«A fA MS ^11 and the liquid surface (fig. 99). This value is the 

53.0 28 9 00.0 o4.4 fiQO '^7 1 <^ n • c \ 

53.5 29.1 63.9 34.5 egj gfj observed hydrometer reading ( Brix) of the 

54.0 29.4 6a2 __"."'" 37^2 ^irup. 

54.5 29.6 64.0 34.5 69.3 37.2 Although most hydrometers are calibrated 

55.0 29.9 64.1 34.6 69.4 37.3 for use at 68" F., this does not mean that sirup 

55.5 30.2 64.2 34.6 69.5 37.3 ^lust be heated or cooled to 68° before its 

56.0 ._.... 30.4 61:4 " - 1^1 Z VZ" 111 density can be measured. Actually, the ob- 

56.5 30 7 64 5 34 8 69.8 37 5 served density can be measured at any temper- 

57.0 30.9 64.6 34.8 69.9 37.5 ature and the true density, or Brix value, calcu- 

57.5 31.2 64.7 34.9 70.0 37.6 lated, if the exact temperature of the sirup at 



MAPLE SIRUP PRODUCERS MANUAL 



87 



the time the reading was made is known. The 
temperature of the sirup should be measured 
with a pi'ecision Fahrenheit thermometer cali- 
brated in intervals of 1.0°, or preferably 0.5°. 
Table 14 shows the amount to be added to or 
subtracted fi'om the observed Brix reading to 
obtain the true density of sirup measured at a 
temperature other than 6S' F. 

The following examples show how to obtain 
the true density of sirup in ° Brix: 

Example 1. What is the true density, in 
° Brix, of sirup having an observed density of 
65.9° Brix at 165° F.? 

Since the observed reading is below 69.9° 
Brix, the correction to use is in column 2 of 
table 14. Locate the temperature 165° F. in 
column 1. Opposite this in column 2 is 5.0° Brix, 
the correction to add to the observed reading. 
Therefore, the true density of this sirup is 65.9° 
+ 5.0°, or 70.9° Brix. 

Example 2. What is the true density of sirup 
having an observed density of 61.0° Brix at 
5r F.? 

Since the observed reading is below 69.9° 
Brix, the correction to use is in column 2 of 
table 14. Locate the temperature closest to 
57° F. (55° F.) in column 1. Opposite this in 
column 2 is 0.5° Brix, the correction to subtract 
from the observed reading. Therefore, the true 
density of this sirup is 61.0° - 0.5°, or 60.5° Brix. 

A<lj listing; Density 

Heavy sirup decreases the potential number 
of gallons of sirup that can be made from a 
quantity of sap. Sirup should, therefore, be 
adjusted to the proper density. Further, sirup 
with a density of more than 67° Brix (more than 
36° Baume at 68° F. or 36.2r Baume at 60° F.) 
must be diluted or it will crystallize on storage. 
The sirup can be diluted either by adding water 
or sap or low-density sirup. 

The amount of water needed to adjust 100 
pounds of heavy sirup, or any part thereof, to 
the standard density of 66.0° Brix is shown in 
table 15. If sap or low-density sirup is used, the 
amount required can be calculated from the 
densities of the two liquids by Pearson's square. 
The calculation is explained on page 126. 

The calculation for adjusting heavy sirup can 
be done accurately only after its true density 
(Brix value) has been determined. 



If the true density of sirup is known, the 
amount of water to add to yield 66'-Brix sirup 
can be obtained directly from table 15. After 
adding the water, stir the sirup well to insure 

Table 14. — Corrections to be applied to ob- 
served Brix readings of maple simp to com.- 
pensate for effects of tem.perature ' 

Correction to subtract from (-) or 
Temperature of added to ( + ) observed Brix reading 
sirup in hydrometer of — 

cup, ° F. 



60.0°-69.9° 



69.9° and higher 



(1) (2) (3) 

° Brix ° Brix 

32 -1.4 -1.5 

,35 -, -1.3 -1.4 

40 -1.2 -1.2 

45 -1.0 -1.0 

50 -.8 -.8 

55 -.5 -.6 

60 -.3 -.4 

65 -.1 -.1 

68- .0 ,0 

70 +.1 +.1 

75 +.3 -I-.3 

80 +.5 +.5 

85 +.8 +.8 

90 +1.0 -1-1.0 

95 -1-1.2 -1-1.2 

100 -1-1.5 -H.5 

105 -1-1.7 -1-1.7 

110 -1-1.9 -1-1.9 

115 -1-2.2 -1-2.2 

120 -1-2.4 -1-2.4 

125 -1-2.7 -1-2.7 

130 -1-3.0 4-2.9 

135 -1-3.2 -H3.2 

140 -1-3.5 -1-3.4 

145 -1-3.8 -1-3.7 

1.50 -1-4.1 -1-4.0 

155 -1-4.4 -1-4.2 

160 -1-4.7 -1-4.5 

165 -1-5.0 -1-4.9 

170 -1-5.5 -1-5.2 

176 -1-5.9 -1-5.7 

' If observed reading is in ' Baume, first convert to 
Brix (p. 85), then apply the temperature correction. 

- Most hydrometers are calibrated at exactly this tem- 
perature. 



AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE 



Table 15. — Water to add to heavy sirup (66.1° to 
70.0° Brix) to obtain 66°-Brix sirup 



True Brix value of 
undiluted sirup ' 



(1) 



Amount of water to add 
to heavy sirup ^ 



Per 100 pounds Per pound 

(2) (.3) (4) 



Fluid 

Pints Ounces ounces 

66.1° 2 0.02 

66.2° 5 .05 

66.3° 7 .07 

66.4° 10 .10 

66.5° 12 .12 

66.6° 15 .15 

66.7° 1 1 .17 

66.8° 1 3 .19 

66.9° 1 6 .22 

67.0° 1 8 .24 

67.1" . 1 11 .27 

67.2° 1 13 .29 

67.3° 2 .32 

67.4° 2 2 .34 

67.5° 2 4 .36 

67.6° 2 7 .39 

67.7° 2 9 .41 

67.8° 2 12 .44 

67.9° 2 14 .46 

68.0° 3 1 .49 

68.1° 3 3 .51 

68.2° 3 5 .53 

68.3° 3 8 .56 

68.4° 3 10 .58 

68.5° 3 13 .61 

68.6° 3 15 .63 

68.7° 4 1 .65 

68.8° 4 4 .68 

68.9° 4 6 .70 

69.0° 4 9 .73 

69.1° 4 11 .75 

69.2° 4 14 .78 

69.3° 5 .80 

69.4° 5 2 .82 

69.5° 5 5 .85 

69.6° 5 7 .87 

69.7° 5 10 .90 

69.8° 5 12 .92 

69.9° 5 15 .95 

70.0° 6 1 .97 

' ° Brix of sirup after correction for temperature. 

" For practical approximations, pints = pounds avoirdu- 
pois, and fluid ounces = ounces avoirdupois. 



that the added water has been uniformly mixed 
with all the sirup. Then check the Brix value of 
the adjusted sirup to be sure that it is the 
correct density (66° Brix). Each additional heat- 
ing causes an additional darkening of the sirup; 
therefore, try to make sirup of the correct 
density when the sap is first evaporated. 

The following examples show how to use 
table 15 in calculating the amount of water to 
add to heavy sirup to yield a 66°-Brix sirup. 

Example 1. A 100-pound sample of heavy 
sirup has a true density of 69.7° Brix. How 
much water should be added to adjust this 
sirup to 66° Brix? 

In table 15 locate 69.7° Brix. Opposite this in 
columns 2 and 3 is 5 pints and 10 ounces, the 
amount of water to add to the 100 pounds of 
heavy sirup to adjust it to 66° Brix. 

Example 2. If only 12 pounds of the sirup in 
example 1 is being adjusted, how much water 
should be added? 

Table 15 column 4 shows that 0.9 fluid ounce 
of water must be added to adjust 1 pound of 
69.7°-Brix sirup to 66° Brix. For 12 pounds, 
12x0.9 or 10.8 fluid ounces of water is required 
to adjust 12 pounds of 69.7°-Brix sirup to 66° 
Brix. 

Example 3. How much water should be added 
to 26 pounds of 68.2f'-Brix sirup to change its 
density to 66° Brix? 

In table 15 locate 68.2° Brix. Opposite this in 
column 4 find the value of 0.53 fluid ounce, the 
amount of water to add to 1 pound of 68.2f-Brix 
sirup. Then, 26x0.53, or 13.8 fluid ounces of 
water is required to adjust 26 pounds of 68.2°- 
Brix sirup to 66° Brix. 

Summary 

(1) Do not check the density of sirup by weight, 
unless precision instruments are available. 

(2) The minimum allowable density is 66.0° 
Brix (at 6? F.) or 35.6° Baume (at 68° F.). 
Sirup that has a density of 66.5° to 67° Brix 
(at 68^ F.) has a higher viscosity and tastes 
better. 

(3) To test the density of sirup with a hydrome- 
ter, fill the can or jar to the top with sirup. 

(4) Use only a clean, dry hydrometer. 

(5) Lower the hydrometer into the sirup care- 
fully until it comes to rest. 



MAPLE SIRUP PRODUCERS MANUAL 



89 



(6) Hold the can so the top is at eye level and 
read the value on the hydrometer scale at 
the surface of the sirup. The value is the 
observed or apparent density of the sirup. 

(7) To determine the true density of the sirup 



from the observed hydrometer reading, 
measure the precise temperature of the sir- 
up and add to, or subtract from, the ob- 
served hydrometer reading, depending on 
how much warmer or cooler than 68" F. the 
sirup is, using table 14. 



GRADING SIRUP BY COLOR 



Color Standards 

Sirup should be graded before it is packaged. 
Vermont producers are required to state on the 
label the grade of sirup they are offering for 
sale to consumers (131). Color is the principal 
grade-determining factor of table sirup that 
meets other requirements, such as density, fla- 
vor, and cloudiness. 

The U.S. Department of Agriculture color 
standards are designated "Light Amber," "Me- 
dium Amber," and "Dark Amber." These corre- 
spond to Bryan Color Nos. 6, 8, and 10. 

The original U.S. color standards were solu- 
tions of caramel in glycerin made according to 
Balch's U) revised spectrophotometric specifica- 
tions for Bryan color Nos. 6, 8, and 10. Master 
sets of these three solutions were supplied each 
year for Federal and State inspection of maple 
sirup. Unfortunately, these caramel solutions 
tend to fade. They should not be kept for use as 
standards for more than 1 year. 

U.S. Color Comparator 

The U.S. Department of Agriculture has de- 
veloped a simple type of color comparator with 
permanent standards of colored glass (9, 10). 
These standards became the official U.S. De- 
partment of Agriculture color standards for 
maple sirup in 1950 and were adopted by the 
Association of Official Agricultural Chemists 
(153). The colors of the different gi-ades of sirup 
are given in table 16. A thick layer of the sirup 
to be tested is placed in the comparator (fig. 
100). This aids in precise grading because the 
standards are widely spaced on a color scale 
when viewed in this thickness. The square con- 
tainer provides a field of view of uniform thick- 
ness and color, a feature that was not possible 
with the cylindrical bottles formerly used. 

The three clear blanks supplied with the 
color-grading kit are placed in the compart- 




PN-n96 

Figure 100. — Color-grading kit. The kit consists of the 
official USDA permanent glass color standard mounted 
in a comparator. The three clear blanks are in position 
in the compai-ator. For viewing, the sirup sample in the 
bottle to the right of the comparator is mounted in one 
of the two openings in the comparator. 

Table 16. — Grade designations of maple sirup, 
as determined by color 



Grade designation 



Color 



Color index 
range ' 



U.S. Grade AA 

(New York 

Fancy or 

Vermont Fancy). 
U.S. Grade A (New 

York No. 1 or 

Vermont A). 

U.S. Grade B (New 
York No. 2 or 
Vermont B). 

Unclassified (New 
York No. 3 or 
Vermont C). 



As light as or lighter 
than Light Amber. 



Darker than Light 
Amber but as light 
as or lighter than 
Medium Amber. 

Darker than Medium 
Amber but as light 
as or lighter than 
Dark Amber. 

Darker than Dark 
Amber. 



■ For description of color index, see p. 45. 

ments in back of the three standard glasses: 
Light; Medium; and Dark Amber. 

The sirup to be graded is poured into one of 
the clean square glass bottles and placed in one 
of the two open compartments. The comparator 
is held at a convenient distance from the eye 



AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE 



90 

and is viewed toward the sky but away from 
the sun (fig. 101). The color grade (classification) 
of the sirup is determined by comparing the 
samples with the standards. If the sample of 




PN-n97 

Figure 101.— The sirup and color standards are viewed 
toward the sky (away from the sun), preferably toward 
the north sky. 



sirup is cloudy, its true color classification may 
be difficult to determine because its brightness 
will be lowered. 

Information concerning the color-gi-ading kit, 
including the comparator block with glass 
standards, may be obtained by writing to the 
Pi-ocessed Products Standardization and In- 
spection Branch, Agricultural Marketing Serv- 
ice, USDA, Washington, D.C. 20250. 

Suininai7 

(1) Color is the grade-determining factor for 
table sirups that meet all other require- 
ments such as density, flavor, and cloudi- 
ness. 

(2) Grade the color of the sirup by visually 
comparing it with color standards. 

(3) Use as standards either the U.S. Depart- 
ment of Agi-iculture permanent glass stand- 
ards (preferred) or suitable caramel-glycerin 
solutions. 

(4) Do not use caramel-glycerin standards that 
are more than 1 year old. 

(5) Designate the color of the sirup as either 
Light Amber, Medium Amber, Dark Amber, 
or Darker Than Dark Amber. 



PACKAGING 



The graded and clarified sirup with a density 
between 66° and 67° Brix at a temperature of 
68f F. is ready for packaging (fig. 102). If the 
temperature of the sirup when tested after 
filtering is still above 180°, the sirup can be 
packaged immediately. If the sirup has cooled 
below 180°, it must be reheated. However, the 
sirup may become darkened if the temperature 
goes above 200° when it is reheated. 

As stated previously, maple sirup is a water 
solution. Like water, sirup expands and con- 
tracts with changes in temperature. For this 
reason it is difficult to package hot sirup accu- 
rately by volume. Accurate packaging 'can be 
done only if the sirup is adjusted to that tem- 
perature for which the volume of the can will 
hold an exact gallon. Since standard-density 
sirup weighs the same regardless of its temper- 
ature, it is best to package maple sirup by 
weight! The sirup can be weighed on ordinaiy 
household scales. However, it is advisable to 



test the scales before they are used. This can be 
done by taking the scale to a gri-ocery store and 
comparing it with the grocer's certified scales. 
To do this, weigh an object that weighs exactly 
1, 2, or 10 pounds (such as a bag of sugar or a 
can of water) on the gi'ocer's scale. Then weigh 
it on the scale being tested. If possible, adjust 
the household scale to make it read correctly. If 
it cannot be adjusted, make a calibration chart 
by recording in one column the household scale 
reading and in the other the corresponding true 
weight. 

When packaging sirup by weight, allowance 
must be made for the weight of the container. 

After the container has been filled with the 
correct weight of sirup, it is sealed and laid on 
its side so that the hot sirup contacts the 
closure and pasteurizes it. After the containers 
have been on their sides 10 to 15 minutes, they 
are readv for cooling. 



MAPLE SIRUP PRODUCERS MANUAL 



91 




PN-479H 

Figure 102. — Sirup being packaged in lithographed cans. 

Stack BiiiTi 

If packaged sirup is stacked while it is still 
hot, the same browning reaction that occurred 
in the evaporator will continue and darken the 
sirup by as much as one or two grades. This 
seldom occurs with fancy grades of sirup. De- 
velopment of color in hot packaged sirup is 
called stack bum. To prevent stack bum, the 
containers should be temporarily stacked with 
an air space to allow air to circulate, and a fan 
should be used to speed up cooling. After the 
cans have cooled to room temperature, they can 
be close packed. 

Control of \Iiero-Org;anisins 

Standard-density sirup will not support ac- 
tive growth of micro-organisms with the excep- 
tion of a few types of yeast and one or two types 
of bacteria. Because of the possible contamina- 
tion of sirup with these organisms, sirup that is 
offered for sale to the consumer should be 
packaged hot. The sirup must be heated to at 
least 180° F. and then packaged immediately 
(27). 



Everyone has seen mold growing on sirup. 
However, mold will not grow in standard-den- 
sity sirup. These apparently contradictory 
statements are explained as follows: Cold- 
packed maple sirup may contain mold spores. 
The mold spores, like the spores of most yeast 
and bacteria, will remain in a resting state and 
will not germinate as long as all the sirup is of 
standard density. 

Sirup stored under ordinary conditions usu- 
ally undergoes some temperature change. 
When the storage temperature increases, some 
of the water of the sirup is distilled up into the 
head space of the container. When the storage 
temperature decreases, this vapor condenses 
into small drops of water that run down onto 
the surface of the sirup and produce a layer of 
low-density sirup in which mold and other types 
of spores can vegetate and grow. 

Even though the sirup contains spores, their 
growth can be prevented by momentarily in- 
verting the packaged sirup once or twice 
weekly (7J^). This destroys the layer of dilute 
sirup and thus inhibits germination of the mold 
spores. 

Although sirup is packaged under clean, sani- 
tary conditions, this does not guarantee that 
the sirup will not become inoculated with micro- 
organisms if it is packaged cold. Once mold or 
yeast has grown in the area where cold packag- 
ing is done, it is almost impossible to package 
sirup by the cold method without its becoming 
infected. 

Chemical inhibitors have long been used for 
preserving foods. Studies (30) have shown that 
one of these, the sodium salt of propyl parahy- 
droxybenzoate (PHBA), is effective in control- 
ling growth of yeast and mold in maple sirup. A 
concentration of only 0.02 percent is required. 
Sodium propyl PHBA is available commercially 
under different trade names. 





CAUTION 


Before iisin 


g this 


or any other chemical 


preservative. 


detei 


■mine whether it has 


been approved by 


your Slate for use in 


intraslate sal 


's and 


by the Federal Foo<l 


and Drug Atl 


minis! 


ration for use in inter- 


stale sales. 







AGRICULTURE HANDBOOK 134, U.S. DEFF. OF AGRICULTURE 



92 

Bulk-stored sirup can be kept free from sur- 
face infection with spoilage micro-organisYns by 
irradiating the surface of the sirup with germi- 
cidal lamps that emit low ultraviolet radiation, 
particularly in the region of 260 millimicrons 
{133). The lamps must be mounted to illuminate 
the entire surface of the sirup (chart 21). 



CAUTION 

Never expose the eyes to radiation fi-om 
gennieidal lamps sinee pennanent dam- 
age ean result. Always turn tli«' lights off 
before working in the area illuminated hy 
these lamps. 



Size and Type of Paekage 

The size and type of package are important 
when sirup is made for retail sale. Housewives 
dislike to repackage sirup from a gallon con- 
tainer to smaller ones for use as occasion de- 
mands. This has been demonstrated by the 
growing tendency on the part of the public to 
buy maple sirup in quart or even smaller pack- 
ages. 

The net weights for standard-density sirup 
are: 1 gallon weighs 11 pounds; 1 quart weighs 
2 pounds and 12 ounces; 1 pint weighs 1 pound 
and 6 ounces. Since sirup must be packed hot 
(180° F. or above), the capacity of the container 
must be at least large enough to allow for the 
volume of the heat-expanded sirup. The volume 
of 11 pounds of standard-density sirup is 231 
cubic inches at 68° F. (20° C); its volume at 
212° F. is 239.9 cubic inches. Thus, a gallon 
container should have a minimum capacity of 
241+1 cubic inches; quart containers, 60.2t0.5 
cubic inches; and pints, 30.1±0.5 cubic inches. 

Consumers expect sirup to be as attractively 
packaged as other foods (fig. 103). When sold at 
roadside stands, sirup packaged in tin con- 
tainers is attractive to tourists regardless of 
the size of the container, because they do not 
have to take special care in storing tin con- 
tainers in the car as they must with glass 
containers. All metal containers should be care- 
fully inspected before they are filled to be sure 
they are free of all foreign matter and contain 
no insects or rodents or their debris. 



ULTRAVIOLET 
TUBE 



REFLECTOR 



COVER 




Chart 21. — Ultraviolet (germicidal) lamp must be posi- 
tioned to illuminate the entire surface of the sirup. 
More than one lamp may be required. 

Both glass and tin packages should be attrac- 
tively labeled. The printed label must be put on 
squarely, and the outside must be clean. Many 
producers are finding that cans with the labels 
lithographed on the tin make an ideal package. 

Suiiiiiiai^ 

(1) Package sirup hot (180° F. or above). 

(2) Do not reheat sirup above 200°. 

(3) Fill sirup package by weight rather than 
by volume. 

(4) In packaging by weight, allow for the 
weight (tare) of the container. 

(5) Use scales that have been tested and cali- 
brated against certified weights. 

(6) Avoid stack bum by cooling the packaged 
sirup before close stacking it. 

(7) Control mold gi-owth in cold-packed sirup 
or in sterile sirup that has been opened 
and exposed to infection by inverting the 
container once a week. 

(8) Yeast spoilage can be prevented only by 
hot packing. 

(9) The chemical inhibitor sodium propyl 
PHBA in 0.02- percent concentration is ef- 
fective in controlling mold and yeast 
growth in sirup. CAfT/O.V— Obtain State 
and Federal approval before use. 



MAPLE SIRUP PRODUCERS MANUAL 



93 




Figure 103. — Maple sirup can be packaged in a variety of containers. 

(12) Package sirup in small containers such as 
quarts, pints, and one-half pints, as well as 
gallons and one-half gallons. 



(10) Use germicidal lamps to irradiate surface 
of sirup in bulk storage to prevent spoilage. 

(11) Package sirup neatly in attractive con- 
tainers. 



STANDARDS FOR MAPLE SIRL P FOR RETAIL SALE 



Maple sirup producers often find it profitable 
to sell their sirup directly to consumers. In 
doing so, farmers not only are producers; they 
also are food processors. As food processors, 
they are expected to offer for sale a product 
that meets Federal and State requirements, 
and they must package their sirup so that it 
will compare favorably in appearance and qual- 
ity with other luxury food items. 

Vermont has taken the lead in the United 
States in enacting regulations governing the 
sale and labeling of maple products {131). New 
York (83) and Wisconsin {138), among other 
States, are establishing similar regulations. To 
obtain information regarding your State regu- 
lations governing the sale of maple products, 
write to the Division of Mai'kets, Department of 



Agriculture, at your State capital. These regu- 
lations protect the buyer and assure him that 
the product he has purchased meets certain 
minimum standards. They also protect the pro- 
ducer against unfair competition. 

The United States standards for table maple 
sirup (129) are as follows: 

UNITED STATES STANDARDS FOR 
GRADES OF TABLE MAPLE SIRUP 

Effective May 24, 1967 
Product Description 

(a) "Maple sirup" means sirup made by the evaporation 
of maple sap or by the solution of maple concrete (maple 
sugar) and contains not more than 35 percent of water, 
and weighs not less than 11 pounds to the gallon (231 
cubic inches). 



94 



AGRICULTURE HANDBOOK 1.34, U.S. DEPT. OF AGRICULTURE 



(b) The standards in this subpart are issued for the 
purpose of classifying maple sirup packed in containers 
for table use. It is not intended that they shall apply to 
sirup which is packed in drums or other large containers 
for later reprocessing. Another set of standards entitled 
"U.S. Standards for Maple Sirup for Reprocessing" has 
been issued for this purpose (§ § 52.5921-62.5926). 

Grades 

U.S. Grade AA (Fancy) . 

U.S. Grade AA (Fancy) Table Maple Sirup shall consist 
of maple sirup which meets the following requirements: 

(a) The color shall not be darker than light amber as 
represented by the color standards of the U.S. Depart- 
ment of Agriculture. 

(b) The sirup shall not be cloudier than light amber 
cloudy standard as represented by the standards of the 
U.S. Department of Agriculture for cloudiness. 

(c) The weight shall be not less than 11 pounds per 
gallon of 231 cubic inches at 68 degrees F. corresponding 
to 65.4' degrees Brix or 35.27 degrees Baume (Bureau of 
Standards Baume scale for sugar solutions, modulus 145). 

(d) The sirup shall possess a characteristic maple flavor, 
shall be clean, free from fermentation, and free from 
damage caused by scorching, buddiness, any objectiona- 
ble flavor or odor or other means. 

U.S. Grade A 

(a) U.S. Grade A Table Maple Sirup shall consist of 
maple sirup which meets the requirements for U.S. Grade 
AA (Fancy) Table Maple Sirup except for color and cloudi- 
ness. 

(b) The color shall not be darker than medium amber as 
represented by the color standards of the U.S. Depart- 
ment of Agriculture. 

(c) The sirup shall not be cloudier than medium amber 
cloudy standard as represented by the standards of the 
U.S. Department of Agriculture for cloudiness. 

U.S. Grade B 

(a) U.S. Grade B Table Maple Sirup shall consist of 
maple sirup which meets the requirements for U.S. Grade 
AA (Fancy) Table Maple Sirup except for color and cloudi- 
ness. 

(b) The color shall not be darker than dark amber as 
repre.sented by the color standards of the U.S. Depart- 
ment of Agriculture. 

(c) The sirup shall not be cloudier than dark amber 
cloudy standard as represented by the standards of the 
U.S. Department of Agriculture for cloudiness. 



' The density requirement was changed in 1974 to 66.0° 
Brix {130a). 



Unclassified 

Unclassified Table Maple Sirup shall consist of maple 
sirup which has not been classified in accordance with the 
foregoing grades. The term "Unclassified" is not a grrade 
within the meaning of the standards in this subpart but 
is provided as a designation to show that no definite 
grade has been applied to the lot. 

Tolerance, Packing 

Tolerances for preceding grades 

In order to allow for variations incident to proper 
grading and handling, not more than 5 percent, by count, 
of the containers in any lot may have sirup below the 
requirements for the grade: Provided, That no part of this 
tolerance shall be allowed for defects causing "serious 
damage": And provided further. That no tolerance is 
permitted for sirup that is darker in color than that 
which is required for the next lower grade. 

Packing 

(a) Containers shall be clean and new in appearance. 
Tin containers shall not be rusty. 

(b) In order to allow for variations incident to proper 
packing, not more than 5 percent, by count, of the con- 
tainers in any lot may fail to meet these requirements. 

Explanation of Terms 

(a) "Cloudiness" means presence in suspension of fine 
particles of mineral matter, such as malate of lime, 
"niter," "sugar sand," or other substances that detract 
from the clearness of the sirup. 

(b) "Clean" means that the sirup shall be practically 
free from foreign material such as pieces of bark, soot, 
dust, and dirt. 

(c) "Damage" means any defect that materially affects 
the appearance or the edibility or shipping quality of the 
sirup. 

(d) "Serious damage" means any defect that seriously 
affects the edibility or market value of the sirup. Badly 
scorched sirup, buddy sirup, fermented sirup or sirup that 
has any distasteful foreign flavor or disagreeable odor 
shall be considered as seriously damaged. 

Summary 

(1) Sirup sold directly to the consumer must 
meet State and Federal specifications. 

(2) The package and label must meet State and 
Federal specifications. 

(3) Know your State law and Federal specifica- 
tions governing the retail sale of maple 
products. 



\1APLE PRODUCTS 



Many producers have found that the gross 
returns of their maple crop can be increased 
fi'om 20 to 160 percent by converting their sirup 



to sugar or to confections such as maple cream, 
soft sugar candies, and maple spreads. The 8 
pounds of sugar in a gallon of sirup is worth $1 



MAPLE SIRUP PRODUCERS MANUAL 



95 



a pound, based on sirup selling at $8 per gallon. 
This same weight of sugar, if converted to 
sugar products, can be sold at prices ranging 
from $1.50 to $2.50 per pound or a gross of $12 
to $20 per gallon of sirup. This increase in gross 
returns is usually more than commensurate 
with the additional labor involved in converting 
sirup to sugar products. 

Equipment 

Making the different maple sugar products is 
not difficult, nor does it require expensive or 
unusual equipment. It does require the same 
type of care and sanitation that is expected of 
any candy company. Maple confections should 
be made in a special room, either in the home 
(fig. 104) or in a part of the evaporator house 
(fig. 105). In some States the law specifies that 



confections for sale cannot be made in the home 
kitchen. 

High-pressure steam is the ideal source of 
heat for evaporating sirup in making confec- 
tions. High-pressure steam heat can be easily 
and instantaneously controlled; and, unlike 
other types of heat, there is no danger of 
scorching the sugars. When steam is not availa- 
ble, gas is preferred. Gas heat is also easily 
controlled (fig. 106). Bottled gas is available 
almost everywhere. 

The size of the equipment (kettles, mixers, 
and pans) depends on the amount of sirup to be 
pi-ocessed. A thermometer with a range of 200° 
to .300° F. in 1° units is a necessity; it can be 
either a dial thermometer or a candy thermom- 
eter. Other equipment includes measuring cups, 
wooden ladles, wooden paddles, and a house- 




Figure lOi.—A porch converted to a candy kitchen and salesroom. 



96 



AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE 




F'N-IK(I1 

Figure 105. — A separate room built in the evaporator 
house makes an ideal candv kitchen. 




PN-4802 

Figure 106. — Gas, whether supplied from tanks or mains, 
is a good source of heat for cooking maple products. The 
heat is.easily controlled and can be stopped the instant 
cooking is completed. Here, sirup is being cooked for 
maple cream. 



hold scale. Provision should be made for cooling 
the sugar products. This is especially desirable 
when making maple cream, fondant, or crystal- 
coating sirup. The cooler for cream can be a 
trough with circulating cold water into which 
the pans of cooked sirup are placed. A pan of 
chipped ice or ice water may also be used. For 
crystal-coating sirup, an insulated box, such as 
a used refrigerator from which the cooling unit 
has been removed, may be used. 

Mapir .Siifiar 
('ln'ini.ttry of Mii/ilf Siifiar 

Maple sirup is essentially a solution of su- 
crose in water. The amount of sugar that can 
be in true solution in a given volume of water 
varies with the temperature of the solution ill, 
12, 51, 82). Hot solutions can contain more sugar 
and cool solutions less sugar. 

Maple sirup solutions containing 67 percent 
of sugar (67° Brix) are saturated at room tem- 
perature (68° F.). That is, no more sugar can be 
dissolved in the solution at that temperature. 
Sirup that has been heated to raise the boiling 
point of the sirup to 7.5° F. or more above the 
boiling point of water will be supersaturated 
when it cools to room temjierature; it will con- 
tain more than 67 percent of sugar. This super- 
saturated sirup, with its excessive sugar con- 
tent, is in an unnatural or abnormal condition, 
and it tends to return to normal by ridding 
itself of the excess sugar so that the sirup will 
again contain only 67 percent of sugar. The 
excess sugar is forced out of solution (precipi- 
tated), and sugar crystals are formed. The 
slower this occurs, the larger the sugar crys- 
tals. 

To make any of the maple sugar products, it 
is necessary first to make supersaturated sirup. 
The degree of supersaturation is increased as 
the boiling temperature of the sirup is in- 
creased and more water is evaporated from the 
sirup. When the amount of supersaturation is 
small and cooling is slow and is accompanied by 
little or no agitation, the state of supersatura- 
tion may persist for a longtime; and little sugar 
will be precipitated. When the amount of super- 
saturation is appreciable, as when sirup is 
boiled 'to 18° F. or more above the boiling }X)int 
of water (11° or more above that of standard- 



MAPLE SIRUP PRODUCERS MANUAL 



97 



density sirup), the sirup will appear to solidify 
on cooling. This solid cake is mostly sugar, but 
some liquid sirup (mother liquor) is mixed with 
the sugar. 



Fornintion of Crystal Sugar 

The crystalline or grainy nature of the pre- 
cipitated sugar is determined by a number of 
factors, all of which are influential in making 
the desired type of confection (8i). These factors 
include the degree of supersaturation, seeding, 
the rate of cooling, and the amount and time of 
stirring. 

Large crystals called rock candy, which rep- 
resent one extreme, are formed when slightly 
supersaturated sirup (67° to 70° Brix) is cooled 
slowly and stored for a long time without agita- 
tion. A glasslike noncrystalline sirup represents 
the other extreme. This is formed when highly 
supersaturated sirup (the boiling point is ele- 
vated ISf F. or more above the boiling point of 
water) is cooled rapidly to well below room 
temperature without stirring. The sirup be- 
comes so viscous that it solidifies before crys- 
tals can form and grow. If the hot supersatur- 
ated sugar solution is stirred while it is cooling, 
the tendency to form crystals increases. The 
mechanical shock produced by the stirring 
causes microscopic crystal nuclei to fonn. Con- 
tinued stirring mixes the crystals throughout 
the thickened sirup, and they grow in numbers 
and in size. When the number of crystals is 
relatively small, stirring causes the largest 
crystals to grow larger at the expense of the 
smaller ones. Thus, a grainy sugar tends to 
become more grainy the longer it is stirred. 

To produce maple sugar with crystals that 
are imperceptible to the tongue (impalpable), 
the crystals must be kept very small, even 
microscopic in size. This is accomplished by first 
suddenly cooling a hot, highly supersaturated 
sirup so that a viscid, noncrystalline, glasslike 
mass is obtained. Then while it is still in the 
supei'saturated state, fine crystals, called seed, 
are added to serve as nuclei, and stirring is 
begun. Since the mass is so highly supersatur- 
ated, billions of tiny crystals are formed at the 
same time, and the result is a very fine grained 
pi'oduct. 



Invert Siigiir 

Although sucrose is the only sugar in sap as 
it comes from the tree, some of the sucrose is 
changed into invert sugar as a result of micro- 
bial fermentation during handling and process- 
ing. Both sucrose and invert sugar are made up 
of two simple sugars, dextrose and levulose. In 
sucrose, these sugars are united chemically as a 
single molecule; in invert sugar, they occur as 
separate molecules. 

A small amount of invert sugar is desirable in 
maple sirup that is to be made into maple sugar 
and maple confections. Invert sugar tends to 
reduce supersaturation, that is, more sugar can 
be held in solution before crystallization occurs. 
This helps keep the product moist (62). Also, it 
encourages the formation of exceedingly small 
sugar crystals. But too little invert sugar in the 
sirup will cause the product to be grainy; too 
much may prevent formation of crystals 
(creaming) as required for making maple 
cream. In general, all grades of maple sirup 
contain some invert sugar, the amount varying 
with the different grades. Fancy has the least; 
and U.S. Grade B or unclassified, the most. 
Thus, the grade of sirup should be a determin- 
ing factor in selecting sirup for making a spe- 
cific confection. 

A simple chemical test to determine the 
amount of invert sugar in maple sirup is de- 
scribed on page 113. If the amount of invert 
sugar in the sirup is so small that a fine 
crystalline product cannot be made, a "doctor" 
solution is required (60). 

'^Doctor" Solutions 

The simplest "doctor" solution and the one 
most commonly used is U.S. grade B pure 
maple sirup, which is naturally rich in invert 
sugar (more than 6 percent, as determined by 
the chemical test described on p. 113). As a rule, 
dark sirup made from sap produced during a 
warm spell contains a high percentage of invert 
sugar. The addition of 1 pint of this doctor sirup 
to 6 gallons of maple sirup low in invert sugar 
(less than 1 percent) usually will correct invert 
deficiency. 

When sirup with a high content of invert 
sugar is not available, the doctor solution can 
be prepared as follows: To 1 gallon of standard- 



98 



AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE 



density maple sirup add 2V2 liquid ounces of 
invertase (an enzyme that causes the inversion 
of sucrose to invert sugar). Stir the mixture 
thoroughly and allow it to stand at room tem- 
perature (65° F. or above) for several days. Dur- 
ing this time sufficient invert sugar will form so 
that 1 pint of this solution can be used to doctor 
6 gallons of maple sirup low jn invert sugar. 
Invertase may be purchased from any of the 
confection manufacturers. 

Another convenient type of doctor is an acid 
salt such as cream of tartar (potassium acid 
tartrate). Addition of V2 teaspoon of cream of 
tartar to 1 gallon of low- in vert sirup just before 
it is boiled for candymaking will cause sufficient 
acid hydrolysis or inversion of the sucrose to 
form the desired amount of invert sugar. 



Maple Cream or Butter 

The amount of the maple sirup crop that is 
being converted into maple cream or butter has 
been increasing rapidly. Some producers have 
built up so large a demand for this confection 
that they convert their entire sirup crop to 
cream. Some producers make from 2 to 3 tons of 
this confection annually. 

Maple cream (8i, 85), a fondant-type confec- 
tion, is a spread of butterlike consistency. It is 
made up of millions of microscopic sugar crys- 
tals interspaced with a thin coating of satu- 
rated sirup (mother liquor). The crystals are 
impalpable to the tongue and give the cream a 
smooth, nongritty texture. The first step in 
making maple cream is to make a supersatur- 
ated sugar solution. This solution is cooled to 
room temperature so quickly that crystals have 
no chance to form. The cooled, glasslike mass is 
then stirred, which produces the mechanical 
shock necessary to start crystallization. 

Sirup for Creaming 

For best results, U.S. Grade AA (Fancy) or 
U.S. Grade A (No. 1) maple sirup should be used. 
However, any sirup may be used provided it 
contains less than 4 percent of invert sugar. 

Invert Sugar Content 

The amount of invert sugar in the sirup 
selected for creaming should be determined by 
the simple chemical test described on page 113. 



Sirup that contains from 0.5 to 2 percent of 
invert sugar should make a fine-textured cream 
that feels smooth to the tongue. Sirup with 
from 2 to 4 percent of invert sugar can be made 
into cream by heating it to 25° F. above the 
boiling point of water (instead of the usual 22° 
to 24°). Sirup with more than 4 percent of invert 
sugar is not suitable for creaming. It will not 
crystallize, or it will crystallize only if heated to 
a much higher-than-normal temperature. How- 
ever, the cream will be too fluid and probably 
will separate a few days after it is made. 

The belief throughout the maple- producing 
area that maple cream should be made only 
from first-run sirup and that all first-run sirup 
will yield a good cream is false. It is the amount 
of invert sugar in the sirup that determines its 
suitability for creaming, not the run of sap from 
which the sirup is made. The amount of invert 
sugar formed is directly proportional to the 
amount of microbial fermentation of the sap. 
This, in turn, is related to the temperature. 
Unseasonably warm weather is not uncommon 
during the first period of sap flow. Warm 
weather favors fermentation of the sap, and 
sufficient invert sugar is produced to make the 
early-run sirup unsuitable for making into 
cream. 

Since most Fancy and Grade A sirup nor- 
mally contains an adequate amount of invert 
sugar, the use of a doctor solution is not recom- 
mended. The addition or formation of too much 
invert sugar will ruin the sirup. Sirup for 
creaming should be selected on the basis of the 
quick test for invert sugar. 

Cooking an(t Cooling 

The sirup is heated to a temperature 22° to 
24° F. above the boiling point of water (37). (The 
temperature of boiling water must be estab- 
lished at the time the sirup is boiled for cream- 
ing.) The boiling temperature indirectly adjusts 
the amount of sirup (mother liquor) left sur- 
rounding the crystals; this, in turn, governs the 
stiffness of the final product. As soon as the 
boiling sirup reaches the desired temperature, 
it should be removed from the heat and cooled 
quickly. If the cooked sirup is left on the hot 
stove (even with the heat turned off), enough 
additional water will be evaporated to produce 
a more concentrated sirup than desired. 



MAPLE SIRUP PRODUCERS MANUAL 



99 



Rapid cooling is necessary to prevent crystal- 
lization. To provide a large cooling surface, the 
sirup is poured into large, flat-bottom pans. The 
layer of sirup should be not more than 1 to 3 
inches deep. The pans are set in a trough 
through which cold water (35° to 45° F.) is flow- 
ing (fig. 107). 

The sirup is cooled to at least 70° F., and 
preferably to 50° or below. It is sufficiently cool 
when the surface is firm to the touch. If crys- 
tals appear during the cooling process, cooling 
is too slow, the pan was agitated, or the invert 
sugar content of the sirup is too low for the 
cooling conditions. This situation can be cor- 
rected either by more rapid cooling (using thin- 
ner layers of sirup or more rapid flow of cold 
water) or by increasing the invert sugar con- 
tent of the sirup by use of a doctor. 

Creaming 

The chilled, thickened sirup should be 
creamed either by hand or mechanically in a 
room having a temperature of 70° F. or above. 
Many producers have developed their own me- 
chanical cream beaters (fig. 108); also, there are 
a number of inexpensive ones on the market. 




Figure 108. — Homemade cream beaters in which the stir- 
rers are held stationary and the pan is rotated at 
approximately 50 r.p.m. 

The homemade maple cream beater (fig. 109) 
consists of a pan approximately 13 inches in 
diameter that holds about 1.5 gallons of cooked 
sirup. In this beater, the scrapers are held 
stationary and the pan revolves at 40 to 50 
revolutions per minute. In other beaters, this 
procedure is reversed. Both types worked 
equally well. 

A hardwood paddle having a sharp edge 2 or 
3 inches wide is used for hand beating (stirring). 
The cooked sirup is poured onto a large flat pan 
such as a cookie tin. The pan is held firmly, and 
the thick sirup is scraped first to one side and 
then to the other. Mixing should be continuous. 




PN-1XU3 

Figure 107. — Sirup that has been concentrated for cream- 
ing is poured immediately into large, flat-bottom pans, 
which are set in flowing cold water to cool to well below 
room temperature. The sirup is sufficiently cool when 
the surface is firm to the touch. 



PN^805 

Figure 109. — At the beginning of the creaming operation, 
the butterlike mass has a shiny surface. When the 
surface becomes dull, creaming is complete. 



100 



AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE 



If stirring is stopped, some of the crystals will 
jji-ow and make the product grritty. 

While being- stirred, the chilled sirup first 
tends to become fluid and then begins to stiffen 
and show a distinct tendency to set. At this 
time the batch loses its shiny surface (fig. 109). 
If creaming is stopped too soon, that is, while 
the batch is too fluid, large crystals will form. 

To hasten the creaming process, a small 
amount of "seed" (previoi^sly made cream) can 
be added to the glasslike chilled sirup just 
before beating. The addition of 1 teaspoonful of 
seed for each gallon of cooked sirup will provide 
crystals to serve as nuclei for the more rapid 
formation of crystals. The entire creaming proc- 
ess may require ft-om 1 to 2 hours, depending on 
the size of the batch, but the use of seed will 
often shorten the time by half. 

Holding Cream for Delayed Packaging 

Often it is not convenient to package the 
cream at the time it is made. In this case, it can 
be stored or aged for periods from 1 day to 
several weeks in tightly covered glass or 
earthen vessels, preferably under refrigeration. 
Many candymakers believe that aging a fon- 
dant is desirable because it permits the crystals 
to equalize in the saturated .sirup. Some pro- 
ducers age the cream 1 day by holding it in an 
open pan covered with a damp cloth; they 
package the second day without rewetting. 
Other producers remelt the aged cream for ease 
of pouring and packaging by carefully heating 
it in a double boiler (99). The temperature of the 
cream during this reheating must not go above 
150° F. (The temperature can be controlled by 
not permitting the water in the double boiler to 
go above 150°.) If the temperature of the cream 
exceeds 150°, too much sugar will be dissolved, 
and large crystals may form when the remelted 
cream is cooled and stored. 

Packaging and Storing 

Maple cream can be packaged in tin, glass, 
plastic, or wax-paper cups. Container with wide 
mouths are best for easy filling. Care must be 
taken to keep air bubbles from forming, espe- 
cially when the cream is packaged in glass 
because the air bubbles are unpleasing in ai> 
pearance and create the impression the pack- 
age is short in weight. Furthermore, air pockets 



provide a place where the separated mother 
liquor can collect, and this also produces an 
unpleasant appearance. 

Fi-eshly made cream should be packaged im- 
mediately, before it "sets up" (fig. 110), or 
within a day if it has been covered and set aside 
to age. Remelted cream should be packaged 
while it is still warm and fluid. Since maple 
cream is a mixture of sugar crystals and satu- 
rated maple sirup, storing packaged cream at 
70° F. or above will cause more sugar to be 
dissolved. The sirup tends to separate as an 
unattractive, dark, liquid layer on the surface 
of the cream. This sirup layer also forms if the 
cream is stored at fluctuating temperatures. 

The cream is best stored at low temperature, 
preferably under refrigeration and at constant 
humidity. If the cream is packaged in glass or 
other moistureproof containers, it can be stored 
in refrigerators for long periods, with little 
danger of the saturated sirup in the cream 
separating. 

Fontlaiit 

Fondant, a nougat-type candy, is known in 
Ohio as maple cream because of its very fine 
crystalline character. Fondant is made in ex- 
actly the same manner as maple cream except 
that the sirup is heated to a higher boiling 
point (27° F. above the boiling point of water). 
The thickened sirup is cooled to 50° and stirred 
as for creaming. Since there is less sirup left in 
the fondant, it will set up to a soft solid at room 
temperatures. Small amounts can be dropped 
on marble slab, waxed paper, or a metal sheet; 
or it can be packed into molds. 

Sofl Sn^ar ('.an<lu's 

Next to maple cream the making of soft 
sugar candies is gaining in popularity. Like 
maple cream, 8 pounds of soft sugar candies 
can be made from 1 gallon of sirup. 

Soft sugar candies contain little or no free 
sirup, so they are stiffer than maple cream. The 
crystals in soft sugar candies are larger than in 
maple cream and are palpable to the tongue, 
but they should not be large enough to produce 
an unpleasant sandy effect. The candies can be 
made from any of the top three grades of sirup: 
U.S. Grade AA (Fancy), U.S. Grade A (No. 1), 



MAPLE SIRUP PRODUCERS MANUAL 



101 




Figure 110. — The finished or remelted cream is suffi- 
ciently fluid to be poured into containers. Use of wide- 
mouthed jars makes filling and emptying easy. 

and U.S. Grade B (No. 2). Unlike maple cream, a 
small amount of invert sugar is desirable be- 
cause it reduces the tendency to produce large 
crystals that give the candies a grainy texture. 
The invert sugar content can be increased by 
adding (1) a doctor solution consisting of 1 pint 
of dark sirup to 6 gallons of table grade maple 
sirup, or (2) a doctor consisting of Vo teaspoon of 
cream of tartar to 1 gallon of low invert sirup. 
Use the quick test for invert sugar to check the 
sirup to be used for candymaking. 

Cooking. Cooling, and Stirring 

The sirup is cooked to 32° F. above the boiling 
point of water established for that time and 
place (fig. 111). The pans of cooked sirup should 
be cooled slowly on a wooden-top table to 
155° F. (as tested with a thermometer). The 
thick sirup should then be stirred, either by 
hand with a large spoon (fig. 112) or with a 
mechanical mbcer. 

While the sugar is still soft and plastic, it is 
poured or packed into rubber molds of different 
shapes. Packing the molds is best done with a 
wide-blade putty knife or spatula (fig. 113). 



Rubber molds for making candies of different 
sizes and shapes can be purchased from any 
maple equipment supplier. Before use, the 
molds should be washed with a strong alkali 
soap, well rinsed, and dried. They should then 
be coated with glycerin applied with a brush. 
Excess glycerin is removed by blotting with a 
soft cloth. If the rubber mold contains too much 
carbon, it will make a mark on the molded 
sugar. To test for too much carbon, rub the 
mold on white paper. 

The Bob. — Another method of preparing the 
sugar so that it can be run into the molds is 
that used by commercial confectioners. After 
stirring, the soft sugar is set aside for a day to 
firm and age. The following day it is mixed with 
an equal amount of "bob," and the mixture is 
run into the rubber molds while it is still fluid. 

The bob (Si ) is sirup that is boiled to exactly 
the same boiling point as used in making the 




Figure HI. — Many types of kettles may be used for 
cooking the sirup for making soft sugar candies. Where 
high-pressure steam is available, a steam-jacketed ket- 
tle is ideal since it permits cooking the sirup without 
danger of scorching. 



102 



AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE 



soft sugar (32° F. above the boiling point of 
water). As soon as the bob is made and while it 
is still hot, the sugar made the previous day is 
added to it, and the mixture is stirred enough 
to get uniformity but not enough to cause it to 




PN_4«0K 

Figure 112. — The thick supersaturated sirup is stirred 
until sugar crystals form and grow large enough to be 
palpable but not large enough to be gritty. 




PN-1K09 

Figure 113. — The partly crystallized sirup is packed into 
molds while it is still plastic. In a few hours crystalliza- 
tion is complete, and the candies are firm and can be 
removed from the molds. 



set up. The hot bob partly melts the sugar, and 
the resulting semiliquid sugar can be poured 
easily. 

Semicontinnous Process. — Ingenuity can be 
used in candymaking. For example, one pro- 
ducer has developed the following semicontin- 
nous process: The sirup is cooked in a special 
vessel (fig. 114) from which the cooled sirup is 
dispensed to a small mechanical agitator (fig 
115). 

Here the sirup is partly crystallized, and 
while it is still fluid it is run into the rubber 
molds where crystallization is completed. It sets 
up in 30 minutes to 1 hour. Candies formed by 
IX)uring rather than packing have an attractive 
glazed surface. 

Crystal Coating 

Candies can be prevented from diying by 
coating them with a moisture-impervious shell 
made from crystalline sucrose (99). The effect of 
ciystal coating soft sugar candies is shown in 
figure 116. The crystallizing sirup is made as 
follows: Fancy maple sirup low in invert sugar 
is heated to 9.5° to IT F. above the boiling point 
of water. This supersaturated sirup should 
have a Brix value of 70P to 73" at a temperature 
of 68^ and 63.5' Brix at 210^ (hot). One gallon of 
standard-density sirup (66° Brix) will make 7 
pints of ci-ystallizing sirup (70^ to 73" Brix). 

The hot, heavy sirup can be set aside to cool 
where it will not be disturbed by jarring or 
shaking, or it can be transferred immediately to 




PN-4H10 

igure 111,. — A special candy-cooking kettle has one end 
shaped like a funnel and is provided with a spout and 
shutoff. After the cooked sirup has cooled but while it is 
still fluid, the kettle is mounted in an upended position 
and the sirup is run out through the shutoff. (Cooker 
designed by Lloyd H. Sipple, Bainbridge, N.Y.) 



MAPLE SIRUP PRODUCERS MANUAL 



103 




PN-1811 

Figure 115. — A continuous candy beater of simple desig^i. 
The cooked sirup is run in a small stream from the 
cooking kettle to the beater, which consists of a rotat- 
ing worm in a metal trough. The worm beats the sirup, 
crystallizes it, and then drives the semiliquid sirup to 
the drawoff cock that controls the flow of the sirup into 
the molds. {Beater designed by Lloyd H. Sipple, Bain- 
bridge, N.Y.) 

large crystallizing pans. To retard surface crys- 
tallization (caused by rapid cooling of the sur- 
face), the sirup should be covered with a piece 
of damp cheesecloth or paper (preferably the 
same kind used as a sirup prefilter, since it has 
a high wet strength). The cloth or paper must 
be in contact with the entire surface of the 
sirup. If crystals form, they will attach them- 
selves to this cover and can be removed along 
with the covering. The sugar crystals can be 
recovered by rinsing the cover in hot water. 

The candies to be coated should be dry (24 
hours old). They can be coated by either of two 
methods. In one method, the candies are loosely 
packed two or three layers deep in a tin pan, 
such as a bread tin, which has a piece of V2- 
inch-mesh hardware cloth in the bottom. The 
covering is removed from the cool (70^ to 8(F F.) 
crystallizing sirup, and any crystals not re- 
moved with the cover are skimmed off. 

In the other method, the candies are loosely 
placed in wire mesh baskets of such size as to 
permit submerging both the baskets and the 



PN^812 

Figure 116. — Crystal-coated candies: Left, Freshly made, 
uncoated candies; center, uncoated candies that have 
been stored 3 months at room temperature — the unat- 
tractive appearance is caused by drying; right, these 
candies, made at the same time as those in the center, 
were coated with sugar crystals, which prevented loss 
of moisture. They have kept the appearance and char- 
acteristics of fresh candies. 

dried candies below the surface of the crystal- 
lizing sirup (figs. 117 and 118). A fresh cover is 
placed directly on and in contact with the entire 
surface of the sirup and left at a temperature of 
65" to 80P F. for 6 to 12 hours, or overnight. This 
is the crystallizing period. The major part of 
the ci-ystal coat forms on the candies during the 
first few hours. Therefore, the time the candies 
are left in the crystallizing sirup beyond a 6- 
hour period is not too critical. Actually, the 
most important factor is the Brix value of the 
crystallizing sirup; if too high, coarse crystals 
result. Sugar comes out of the thick sirup and is 
deposited and grows on the millions of tiny 
crystals on the surface of the candies. The best 
density of the sirup should be determined by 
trial runs. When sufficient sugar has been de- 
posited on the candies, the paper or cloth cover 
is removed, and the wire baskets of coated 
candies are lifted out of the sirup and supported 
above the trays of sirup until the candies have 
drained. 



104 



AGRICULTURE HANDBOOK I'M, U.S. DEPT. OF AGRICULTURE 




PN-4813 

Figure 117. — A french-fryer blanching assembly pro- 
vides a practical means for crystal coating maple candies 
on a small scale. The candies are placed in the basket for 
crystallizing in the thick sirup and are left in the basket 
to drain. The drained sirup is caught in the sirup pan 
and is used for making other lots of candies. 




PN-4814 

Figure 118. — A large crystallizing pan for use in a con- 
stant-temperature cabinet. Hangers are attached for 
suspending baskets for draining candies after crystal 
coating. 



After the sirup has drained from the candies 
(one-half hour), the candies are dried by remov- 
ing all remaining drops of sirup. Failure to do 
this results in areas having a glazed (noncrys- 
talline) surface that is not a water barrier and 
that permits the candies to desiccate (dry out) 
during storage. Desiccated spots appear as 
vk^hite areas. 

The drained candies can be freed of any 
remaining drops of crystallizing sirup by two 
methods. In one method the candies are spread 
out (one layer thick) on a sheet of paper and 
each piece is turned over at intervals of 1 to 2 



hours. In the other method each piece of candy 
is wiped with a damp sponge to remove any 
moist areas. The dry candies are placed on 
trays (fig. 119); the bottoms of the trays are 
made of V4-inch hardware cloth. The trays of 
candies are set in racks to complete the air- 
drying process at room temperature. This usu- 
ally requires from 4 to 7 days. After drying, the 
candies are ready for packaging. Candies 
should not be crystal coated on humid or rainy 
days because they will not diy properly. If 
candies are not thoroughly dried, their coating 
will dissolve when they are packaged. 

The packages have two functions: (1) To 
make the candies as attractive as }x)ssible and 
(2) to keep them in good condition (fig. 120). 
Boxes, individual wrappings, and candy cups 
can be obtained from a confectioner's supply 
house. The net weight of the candies must be 
stated on the outside of the package. This 
requires that the weight of the box (tare) and 
the net weight of the candies be determined for 
each box. 

Candies that have been crystal coated have 
relatively good shelf life; they do not tend to 
take up moisture or to dry out. Candies that are 
not crystal coated may do either, depending on 




PN-4815 

Figure 119. — After the candies have teen removed from 
the cr>-stallizing sirup and wiped, they are put on wire 
screen trays and placed in racks for air drying before 
packaging. 



MAPLE SIRUP PRODUCERS MANUAL 



105 




Figure 120. — Packaging sugar candies, a popular confec- 
tion often used as one of the items in a gift package. 

the humidity of the room in which they ai'e 
stored. In a room of low humidity, they will lose 
moisture. The dried-out areas will appear as 
white spots and will become stonelike in hard- 
ness. If the humidity is high, the candies will 
take up moisture, and moist areas or droplets of 
water will appear on the surface. The droplets 
become dilute sugar solutions and are good 
sites for mold growth. The humidity of the 
packaging room can be controlled by a de- 
humidifier and air-conditioner. Never package 
on rainy days (62). 

The best type of wrapper for the outside of 
the candy package is one that is moistureproof, 
such as metal foil or wax-coated paper. A mois- 
tureproof wrapper helps to prevent changes in 
the candies during storage. Unfortunately, 
most wrappers are not completely moisture- 
proof.. They reduce the gain or loss of moisture 
but do not prevent it, especially if the candies 
are stored under excessively high or low mois- 
ture conditions or for long jieriods. Some pack- 
ers of maple confections obtain longer storage 
by puncturing the moistureproof wi-apper with 
many small holes to permit the package to 
breathe. 



Maple S|u-«'iul 

Maple cream, described on page 98, is not 
stable when stored at room temperature be- 
cause saturated sirup (mother liquor) tends to 
separate from the cream and cover it with a 
sirup layer. 



A new semisolid dextrose-maple spread has 
been developed that prevents this separation of 
sirup. Also, it requires no heating or stirring. 

The process for making the spread consists of 
three simple steps: (1) The sirup is concentrated 
by heating it to a density of 70P to 7S Brix; (2) 
part of the sucrose is converted to invert sugar 
by enzymatic hydrolysis; and (.3) the dextrose 
(part of the invert sugar) is ciystallized to form 
a semisolid spread. 

Standard-density maple sirup (66° Brix) is 
heated to about 1(F F. above the boiling point of 
water (approximately 7(? Brix), and then cooled 
to 15(F or below (as tested with a thermometer). 
While the sirup is still fluid, invertase is added 
at the rate of IV2 ounces per gallon of sirup and 
thoroughly mixed with the sirup by stiiTing. 
The enzyme will be inactivated and hence inef- 
fective if it is added while the sirup is too hot 
(above 16(F F.). The enzyme-treated sirup is 
stored at room temperature for 1 or 2 weeks. At 
first, ci-ystals (sucrose) appear, but they do not 
form a solid cake, and as the hydrolyzing action 
of the enzyme progresses, the crystals dissolve. 
The result is a crystal-free, stable, high-density 
sirup (70° to 78° Brix) containing a large 
amount of invert sugar. This sirup will remain 
clear at ordinary temperatures. Because of its 
high density, it makes an excellent topping for 
ice cream and sirup for waffles or pancakes. 

Maple spread is made by seeding this high- 
density sirup with dextrose crystals. A crystal- 
line honey spread, a stock grocery item, is a 
convenient source of dexti'ose crystals for seed- 
ing the first batch. For additional batches, crys- 
tals from previously made lots of the maple 
spread may be used as seed. The dextrose 
crystals are added at the rate of 1 teaspoon per 
gallon of high-density sirup and thoroughly 
mixed with the sirup. After mixing, the sirup is 
poured into packages and set aside at a temper- 
ature of 55° to 60P F. Within a few days a 
semisolid spread forms. It is stable at tempera- 
tures up to 8(F F. If refingerated, it will keep 
indefinitely without any sirup separating. 

Maple spread eliminates the laborious hand 
beating or the expensive machine beaters re- 
quired for making maple cream. Furthermore, 
the yield of maple spread j^er gallon of sirup is 
higher, because it is made from sirup concen- 
trated to between 7(F and 78° Brix, whereas 



106 



AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE 



sirup for maple cream is concentrated to 8(F 
Brix. 

I liin<Ml Mapl<> IVoiliirl 

In making tlie maple products described in 
the preceding pages, only sirup low in invert 
sugar should be used, except for that used as a 
doctor. These products, therefore, are primary 
uses for the top grades of table sirup, U.S. 
Grade AA, U.S. Grade A, and U.S. Grade B. 

A new maple product called fluff has been 
developed at the Eastern Regional Research 
Center (135). It can be made from the lower 
grades of sirup (sirup high in invert sugar). In 
addition, it has a number of other advantages. 
Some of these advantages are: (1) There is a 
large overrun because the volume of the cooked 
sirup is increased by incorporating air during 
the beating process; (2) the new product con- 
tains a higher percentage of water than does 
maple cream so that a larger volume can be 
made from 1 gallon of standard-density sirup; 
(3) the monoglyceride used in the formula tends 
to reduce its apparent sweetness and make it 
more palatable, but without loss of the maple 
flavor; and (4) the time required to whip it is 
only a fraction of that required for making 
maple cream. The fluffed product has excellent 
spreading properties and has an impalpable 
crystal structure. While there is less tendency 
for the fluff to bleed, it does tend to become 
somewhat grainy, especially if stirred too long. 
This tendency to grain is retarded by storing 
the fluff under refrigeration. 

Makhtfi ihf Fluff From Maplf Siriii> 

Heat the sirup until its temperature has been 
elevated 17° F. above that of boiling water. 
Allow it to cool, with occasional stirring, to 
between 17.5° and 185° F. (as tested with a 
thermometer). Add highly purified monoglycer- 
ide (Myverol 18-00)^ equal to 1 percent of the 
weight of the maple sirup used, that is, 0.11 
pound (Va cup) per gallon or 2 level teaspoonfuls 
per pint. Dissolve the monoglyceride by adding 
it slowly and stirring. If the sirup cools below 
145°, the monoglyceride will not dissolve. Cool to 
between 150P and 160^ and whip the mixture 



' Produced by Distillation Products Industrj'. Roches 
ter, N.Y. 



with a high-speed (household) beater. Fluffing 
should occur within 2 minutes. 

\hikiiifi thf Fluff From Mofflf .Sin/;* nnti 
Moith' Sufior 

To 1 cup of pure maple sirup (any grade) add 
V2 cup of maple sugar and heat the mixture 
until the sugar is completely dissolved. Do not 
boil. Cool to between 175° and 185° F. with 
occasional stirring. Add slowly and stir until 
dissolved 1 teaspoonful of Myverol 18-00 for 
each cup of sirup. Cool to between 15(f and 16(F, 
and whip the mixture with a high-speed (house- 
hold) beater. Fluffing should occur within 2 
minutes. 

The sugar must be completely in solution at 
the time it is whipped to prevent a grainy 
texture. If sugar crystals do form, they may 
be redissolved by heating the suspension; but 
loss of water must be avoided, and no more 
Myverol need be added. 

Excessive heating of the Myverol tends to 
cause it to lose its properties. 

The texture and consistency of the fluffed 
products can be varied as follows: 

(1) Whipping Time. — As time of beating 
lengthens, the stiffness of the product in- 
creases. The initial, thin whip can be used as a 
topping for ice cream or other desserts. The 
stiffer product is an excellent spread or icing for 
baked goods. (The beating time will be affected 
by the temperature of the mixture at the start 
of the beating. The higher the temperature, the 
longer it will take to reach a given consistency.) 

(2) Ratio of Sugar to Wafer.— The higher the 
sugar content of the mixture in relation to the 
water content at the time the sugar-water- 
stabilizer mixture is whipped, the greater the 
consistency of the fluffed product. 

Hi^li-Fla>or<Ml MapK* Sirup 

As stated earlier, the color and flavor of 
maple sirup result from a type of browning 
reaction that occurs between constituents of 
the maple sap during evaporation. Experiments 
have shown that all the potential flavor is not 
developed during the usual evaporation proc- 
ess. {1J,8). To develop maximum flavor, the 
browning reaction must be carried further; that 
is, the sirup must be heated to a higher temper- 
ature and for a longer time. 



MAPLE SIRUP PRODUCERS MANUAL 



107 



Unfortunately, high temperatures favor the 
formation of an acrid "caramel" flavor. The 
presence of large amounts of water favor cara- 
mel formation and the presence of some cara- 
mel in the initial sirup accelerates it (90). There- 
fore, only the two top grades of sirup — U.S. 
Grade AA (Fancy) or U.S. Grade A (No. 1)— 
should be used in making high-flavored maple 
sirup. It may be made by the atmospheric 
process (H9), by the constant-volume pressure- 
cooking process (139)? or by the new continuous 
process. 

High-flavored maple sirup made from U.S. 
Grade AA or U.S. Grade A sirup by either 
process will have a strong full-bodied flavor 
four to five times that of the sirup from which it 
was made, and it will be essentially free from 
caramel. 

The high-flavored process does not concen- 
trate the flavor; instead, it develops more ma- 
ple flavor than present in the original sirup. 

Atmospheric Process 

In the atmospheric process the sirup is con- 
centrated at atmospheric pressure by heating 
to a boiling temperature of 25(y to 255° F. This 
reduces the water content of the sirup to ap- 
proximately 10 percent. The sirup is held at this 
temperature for IV2 to 2 hours. It is then cooled, 
and water is added to replace that lost in 
evaporation so that the sirup is again of stand- 
ard density. 

Because of the low moisture content of the 
sirup during the cooking period, there is danger 
of scorching if it is heated in a kettle on a stove 
or other hot surface. It is recommended, there- 
fore, that the high-flavoring process be con- 
ducted with high-pressure steam in a steam- 
jacketed kettle or in a kettle provided with a 
steam coil (chart 22). 

The first step of the process — removing the 
water from the sirup — should be done as rai> 
idly as possible. Steam pressure of from 30 to 
1(K) pounds should be used. As soon as the sirup 
reaches a temperature of 252" F., the steam 
pressure is reduced until only enough heat is 
applied to maintain the sirup between 25(P and 





TRAP 



DRAIN 



STEAM OR WATER 
CONNECTION 



" Described in U.S. Patent 2,054,873 issued to George S. 
Whitby on September 22, 1936. This patent has expired, 
and the process is now available for free use by the 
public. 



Chart 22. — Kettle with steam coil can be built in any tin 
shop. It is not as convenient to use as a tilting-jacketed 
kettle, but very satisfactory results can be had with it. 
Like the steam-jacketed kettle it must be operated with 
high-pressure steam and the condensed water must not 
be allowed to collect in the coils. Provision should be 
made for running cold water through the coils for 
cooling the sirup. 



255°. Usually a steam pressure of 20 to 28 
pounds is sufficient. A cover is placed over the 
kettle to prevent further loss of water through 
evaporation. The cover need not be airtight. 
Because of the high viscosity of the sirup, little 
water will be vaporized. 

A thermometer calibrated in 1° intervals, 
with a range that includes 250^ to .30(f F., is 
kept in the sirup during the high-flavoring 
process. If the temperature of the sirup rises 
above 255° during the holding period, the steam 
pressure should be decreased. To prevent for- 
mation of crystals, the sirup should not be 
stirred or agitated during the high-flavoring 
process. 

The end of the heating (cooking) period is 
best determined by odor. The cover is lifted, and 
a handful of steam is scooj^ed up and brought 
toward the nose; heating is stopped as soon as 
an acrid caramel odor is detected in the steam. 
Care must be taken not to get a steam burn. 



108 



AGRICULTURE HANDBOOK 184. U.S. DEPT. OF AGRICULTURE 



Always bring the hand to the nose; do not bend 
over the kettle. 

At the end of the cooking period, the thick, 
supersaturated sirup is cooled to I8(f F. Ap- 
proximately 3 pints of water is added for each 
gallon of sirup originally used to replace the 
water lost in evaporation and restore the sirup 
to standard density. Extreme caution must be 
exercised in adding the water because the 
water will be converted to steam with explosive 
violence if the sirup has not cooled to a temper- 
ature below the boiling point of water. 

After addition of the water, the sirup is again 
brought to a boil and heating is continued until 
the temperature reaches that of standard-den- 
sity sirup (7 F. above the boiling point of 
water). 

As flavor and color in sirup develop initially 
to the same degi'ee, flavor development in the 
treated sirup may be measured indirectly by 
measuring the increase in its color. A sample of 
the high-flavored, standard-density sirup is 
weighed and then diluted with a colorless cane 
sugar sirup having a density of 66° Brix as 
measured with a hydrometer or refractometer. 
The colorless sirup is added slowly to the high- 
flavored sirup, with thorough stirring, until the 
mbcture matches the color of the original maple 
sirup. Then the mixture is weighed. The in- 
crease in color and flavor is determined by the 
ratio. 

Weight of mixed sirup 

Weight of high-flavored sirup 

= Increase in flavor 

This procedure can be used to follow the 
progi-ess of the high-flavoring process, since 
different lots of sirup of the same grade develop 
flavor at slightly different rates. A sample is 
removed periodically from the cooking sirup 
and weighed. Enough water is added to restore 
the sample to standard density (66' BrLx), and 
its increase in color and flavor is determined. 
The tests are easy to make; the 2-ounce French 
squai-e bottle supplied with the U.S. color com- 
parator (described on p. 89) is used. The high- 
flavor process and its end uses are shown in 
figure 121. 

l'rfssiir<'-( DoLiiifi I'rnifss 

Many maple producers do not have higli- 
pressure Steam equipment. They may make 



A NEW MAPLE PRODUCT 




■IJ^ 



PN"-48n 

Figure 121.— A schematic drawing showing the high- 
flavoring process and its use in making blended sirup 
and as a food flavoring. 

high-flavored sirup by the pressure-cooking 
process {139}. In this process, standard-density 
sirup is heated in a closed vessel, such as an 
autoclave or ordinaiy pressure cooker, at 15 
pounds' pressure. Best results are obtained 
when the sirup is heated to a temperature of 
25(f to 253° F. as in the atmospheric process. 

In the pressure-cooking process, the water 
content of the sirup is 34 percent during 
heating rather than 10 percent, as in the at- 
mospheric process. The higher water content 
favors formation of caramel. However, the rate 
at which caramel forms depends on the original 
caramel content of the sirup. The higher the 
caramel content in the original sirup, the 
greater the amount formed in the product. 
Since the amount of caramel in sirup is related 
to the amount of color, only U.S. Grade AA 
(Fancy) or U.S. Grade A (No. 1) sirup should be 
used to make high-flavored sirup by the pres- 
sure-cooking process. Darker grades usually re- 
sult in an unpalatable product. 

The sirup is heated almost to boiling and 
immediately is transferred to jars, which are 
filled to vvithin '., inch of the top. The lids are 



MAPLE SIRUP PRODUCERS MANUAL 



109 



set loosely in place, and the jars are placed in 
an autoclave or pressure cooker, which contains 
the amount of water specified by the manufac- 
turer. The cover of the cooker is assembled, and 
steam is generated accordinfi: to the manufac- 
turer's directions. The sirup is heated at 1.5 
pounds' pressure for approximately VI., hours. 
Then the pressure is decreased slowly to zero 
without venting or quenching. The containers 
must not be jarred or the sirup may boil over. 

( .s«>.s' «»y ftifih-h'hit'ored Siriift 

High-flavored sirup has a number of uses. 
Because it is richer in maple flavor, it is ideal 
for making maple products. It is especially de- 
sirable for use in making cream and candies. 
From 1 to 2 percent of invert sugar is formed in 
the high-flavoring process. This is the optimum 
amount to make perfect cream or soft sugar 
candies without the need of a "doctor." High- 
flavored, high-density maple sirup makes a su- 
perior topping for ice cream. 

Only high-flavored sirup should be blended 
with other foods such as maple-flavored honey 
and crystalline honey spreads. Regular maple 
sirup usually does not have enough flavor to 
compete with or to break through the flavor of 
the food to which it is added. An inexjjensive 
table sirup that has the full flavor of pure 
maple can be made by blending 1 part of high- 
flavored, standard-density sirup with 3 parts of 
cane sugar sirup that has a Brix value of 66°. 
Blended sirup must be projDerly labeled when 
offered for sale. The percentage of each ingi-edi- 
ent must appear on the label, with the one in 
greater amount appearing first. 

drvslalliiK' Moncv-Miipli- Spix'ad 

The development of a maple-flavored crystal- 
line honey spread has produced a new farm 
outlet for both maple sirup and honey. This 
spread is made by mixing honey with high- 
flavored maple sirup {81 ). The maple flavor 
must be strong enough to break through the 
honey flavor and tiie siruj) must contain a large 
amount of invert sugar. These requirements 
are met by converting U.S. Grade B (Vermont 
B or New York No. 2) sirup to high-flavoretl 
sirup as described earlier except that the siruj) 
is heated to a temperature W or 2(f F. above 
the boiling point of water. It is then cooled to 



150P or lower, and V/., to 2 ounces of the enzyme 
is added i^er gallon of sirup. The mixture is set 
aside at room temperature until the action has 
been completed, usually about 2 weeks. The 
sirup may have the appearance of soft sugar 
(U5). 

The high-flavored, high-density maple sirup 
is added to mild strained honey at the rate of 33 
parts of maple sirup to 67 parts of honey by 
weight. The mixture is crystallized by the Dyce 
process (21) as follows: The honey-maple mix- 
ture is seeded with crystalline honey (available 
in most gi'ocery stores) or with some honey- 
maple spread from a previous batch, at the rate 
of 1 ounce of seed to 1 quart of honey-maple 
mixture. After thorough stirring, the seeded 
mixture is held at 57° to BOF F. until crystalliza- 
tion is complete, usually 3 to 7 days. The result- 
ing product is smooth, it has a barely percepti- 
ble gT'ainy character, spreads well, and has a 
very pleasing flavor. This spread becomes liquid 
at temperatures above 85°. Therefore, it should 
be stored under refrigeration. 

Maple sirup blends well with honey in mak- 
ing other honey-maple confections. Recipes for 
these can be obtained from Pennsylvania State 
University, University Park, Pa. 16802. 

Other Mapir l*ro<liuts 
Rock Cdinly 

Production of rock candy usually is uninten- 
tional. Although it should not be considered a 
product of maple sirup, this form of "maple 
sugar" is easy to make, as follows: When maple 
sirup is evaporated to a density between 67.5° 
and 7(f BrLx (heated to ST F. above the boiling 
point of water), and the sirup is stoi'ed for a 
considerable length of time at room tempera- 
ture or lower, a few well-defined crystals of 
sucrose (rock candy) appear. These continue to 
grow in size if the sirup is left undisturbed for a 
long time. 

Hard Siignr 

Because it is not easy to eat, hard sugar is 
not classified as a confection. Producers find 
there is a small demand for hard sugar since it 
offers a convenient form for the safe and stable 
storage of maple sirup. The hard sugar cake 
can be broken up and melted in water, and the 



110 



AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE 



solution can be boiled to bring it to sirup den- 
sity. This sirup is called maple-sugar sirup to 
distinguish it from sirup made directly from 
sap. 

Hard sugar is made by heating maple sirup 
to approximately 40P to 45° F. above the boiling 
point of water. As soon as the sirup reaches the 
desired temperature, it is removed from the 
heat and stirred. Stirring is continued until the 
sirup begins to crystallize and stiffen; then the 
semisolid sirup is poured into molds. If stirring 
is continued too long or if transfer of the sugar 
to the molds is delayed, the sugar will solidify in 
the cooking vessel. 

In the past, hard sugar, often called maple 
"concrete," was the preferred form for holding 
commercial maple sirup in storage. 

Granulated (Stirred) Sugar 

Granulated (stirred) sugar is made by heat- 
ing maple sirup to between 40P and 45° F. above 
the boiling point of water, as in making hard 
sugar. The hot, partly crystallized, thickened 
sirup is transferred from the kettle to a stirring 
trough, and it is stirred continuously until 
gi-anulation is achieved. In the past, this form 
of maple sugar was made by stirring it in a 
hollowed log usually made from basswood (fig. 
122). 

Maple on Snoiv 

Maple on snow is a favorite of guests at a 
maple-sirup camp. As in making stirred sugar, 
the sirup is heated to 22^ to 4(f F. above the 
boiling temperature of water. The final temper- 




PN-IKIK 

Figure 122. — Stirred sugar, another popular item, while 
more easily made by stirring the sirup in a steam 
kettle, has often been made by stirring it in a hollowed- 
out basswood log with a wooden hoe. 



ature within this range depends on individual 
preference. As soon as the sirup reaches the 
desired temperature, it is poured immediately, 
without stirring, on snow or ice. Because it 
cools so quickly, the supersaturated solution 
does not have a chance to crystallize; it forms a 
thin, glassy, taffylike sheet. 

Recipes for other maple confections can be 
obtained by writing to your State Department 
of Agriculture or your Extension Service. 



Suimnai'^ 



Maple Sugar 



(1) Converting maple sirup to maple sugar is 
not difficult. The only special equipment 
required for small-scale operations is a ther- 
mometer having an upper range of 250^ to 
300P F. calibrated in 1° units. 

(2) Sirup that is saturated with sugar at one 
temperature will be supersaturated when 
cooled to another temperature. 

(3) Supersaturated sugar solutions tend to re- 
gain their normal or saturated state by 
throwing the excess sugar out of solution. 
This precipitated sugar usually is in the 
form of crystals, and the amount formed 
depends on the degi'ee of supersaturation. 

(4) The size and number of crystals in the 
precipitated sugar depend on the degi'ee of 
supersaturation, the rate of cooling the sir- 
up, and the amount and time of stirring. 

(5) Invert sugar, a product of sucrose, tends to 
retard the crystallization. Its presence in 
maple sirup is usually the result of fermen- 
tation of the sap. It influences the ciystalli- 
zation of maple sugar. Too much invert 
sugar may prevent ciystallization of sugar 
from a supersaturated sirup. Too little will 
cause the maple sugar to be coarse and 
gritty. 

Maple Cream or Butler 

(1) Use a sirup low in invert sugar (0.5 to 2 
percent). U.S. Grade AA (Fancy) or U.S. 
Grade A (No.l) usually meets these specifi- 
cations. 

(2) Test all sirup for invert sugar by the quick 
test. Do not use sirup that contains more 
than 4 percent of invert sugar. 



MAPLE SIRUP PRODUCERS MANUAL 



111 



(3) Heat the sirup to 22 or 2-f F. above the 
boihng: point of water. 

(4) Cool the sirup rapidly to 5(T F. 

(5) Stir the thickened sirup continuously until 
creaming: is completed. 

(6) Freshly made cream can be packed immedi- 
ately or it can be aged before packajering. 

(7) Aged cream can be softened for pouring by 
heating to a temperature not exceeding 
15a F. 

(8) Store the cream under i-efrigieration. 

(9) Causes of failure to cream: 

(a) If the sirup contains too little invert 
sugar or if it is not chilled sufficiently 
before stirring, the cream will have 
gi'itty texture. 

(b) If the sirup contains too much invert 
sugar, it will not cream (crystallize). 

FontUiitl 

(1) Pi-epare as for maple cream, except increase 
the boiling point of the sirup to 2T above 
that for water. 

(2) Stir or beat the sirup as for maple cream. 

(3) Place drops of the semisolid sugar on mar- 
ble slab, waxed paper, or metal sheet — OR — 

(4) Pour the semisolid sugar into rubber molds. 

Soft Sn^iir ('(indies 

(1) Use any of the top three grades of sirup. 

(2) Heat the sirup to 32" F. above the boiling 
point of water. 

(3) Cool the sirup slowly to 155= F. 

(4) Stir the thickened sirup until enough ciys- 
tals have formed to make a soft, plastic 
mass. 

(5) Immediately pour or pack the soft sugar 
into molds — OR — 

(6) Set it aside in a crock at room temperature 
for 24 to 48 hours. 

(7) Concentrate an equal amount of sirup as 
before. 

(8) As soon as the same elevation of boiling 
point (32° F.) is reached, add the hot concen- 
trated sirup (bob) to the aged soft sugar. 

(9) Stir only enough to mix and pour the semi- 
solid sugar into the molds. 

Crystdl Cnatiiifi 

(1) Make crystallizing sirup from top grades of 
maple sirup. 



(2) Concentrate the sirup to a density of l(f to 
7.T Brix by heating it to 9.5" or IT F. above 
the boiling point of water (63.5° Brix hot 
test). 

(3) Cool to room temperature. 

(4) Keep the surface of the sirup covered with 
heavy paper, except when adding or remov- 
ing the candies. 

(5) Place the freshly made candies in the heavy 
sirup and leave them in the sirup 6 to 12 
hours. 

(6) Remove the candies and completely drain 
the sirup from them. 

(7) Place the candies on paper-covered trays 
and turn each piece eveiy hour until diy, or 
wipe with a damp sponge. 

(8) Do not attempt to crystal coat candies dur- 
ing humid or rainy weather. 

(9) Air diy at room temperature 4 to 7 days. 



Maple Spreiiil 

(1) Use any of the three top grades of sirup. 

(2) Heat the sirup to 10= or ir F. above the 
boiling point of water (7Cf to 78" Brix). 

(3) Cool the thick sirup to 150P or below and add 
IV2 ounces of invertase per gallon of sirup. 

(4) Store at room temperature for 2 weeks. The 
resulting product is high-density sirup. 

(5) "Seed" the high-density sirup with dextrose 
crystals from previous batches of spread or 
from ciystallized honey. Use 1 teaspoonful 
per quart of sirup. 

(6) Mix the seed thoroughly through the sirup 
and pour the mixture into the final package. 

(7) Store at 55= to 60F F. Within a few days the 
dextrose ciystals will grow to yield a plastic 
spread. 



Fltiffed Maple Proditvt 

(1) Can use lower grades of sirup. 

(2) Heat the sirup to IT F. above the boiling 
point of water. 

(3) Cool with occasional stirring to 175° to 
185° F. 

(4) Add 1 percent (Vs cup per gallon or 2 level 
teaspoonfuls per pint) of a purified monogly- 
ceride (Myverol 18-00) slowly with stirring. 

(5) Cool to 150f to 160F F., whip 2 minutes with 
a high-speed cake mixer. 



112 



AGRICULTURE HANDBOOK 184, U.S. DEPT. OF AGRICULTURE 



Hifili-h l<iitfrt'«l Mtiplf Sirup 

Use either of the two top grades of sirup to 
make hig:h-flavored maple sirup, and make it by 
either the atmospheric or the pressure-cooking 
process. 

Atmospheric Process 

(1) Concentrate the sirup by heating to 40P F. 
above the boiUng point of water (25Cf to 
255" F.). Pi'ocess only in a steam kettle, jack- 
eted or with coils. 

(2) Hold the thickened sirup at the final tem- 
perature of concentration for IV2 to 2 hours. 

(3) Cover the kettle and reduce the steam pres- 
sure to approximately 24 or 26 pounds per 
square inch — to keep the sirup at 252" to 
255° F. 

(4) Turn off the steam at the end of the proc- 
essing period and cool the thick sirup to 
180F F. 

(5) Add water with caution and in small 
amounts until the sirup is restored to about 
standard density and reboil to T F. above 
the boiling point of water. 

Pressure-Cooking Process 

(1) Heat the sirup almost to boiling tempera- 
ture (210F to 215= F.). 

(2) Transfer to containers to fit the cooker (usu- 
ally 1- or 2-quart jars). 

(3) Place the lids on the containers loosely, and 
put them in the cooker. 

(4) Add water to the cooker according to the 
manufacturer's directions and secure the 
cooker lid. 

(5) Bring the steam pressure in the cooker to 
15 pounds per square inch. Hold at this 
pressure for V/2 hours. 

(6) Allow the pressure to fall slowly; do not 
vent or quench. 

(7) When the pressure has fallen to zero, open 
the cooker and remove the high-flavored 
sirup. 



(.rvshilliiit' Hiniry- Maplf Sinriiil 

(1) Use U.S. Grade B, Vermont B, or New York 
No. 2. sirup. 

(2) Heat the sirup to 19^ or 2Q F. above the 
boiling point of water (80P Brix). 



(3) Cool the thick sirup to below 150P F. and add 
IV2 to 2 ounces of invertase per gallon of 
sirup. 

(4) Store at room temperature for 2 weeks to 
produce a high-density sirup. 

(5) Mix thoroughly one part of the high-density 
sirup to two parts of mild flavored honey. 

(6) Add seed (dextrose crystals) at the rate of 1 
teaspoonful per gallon of mixture. Use a 
previous batch of honey-maple spread or 
crystalline honey as seed. 

(7) Hold the seeded mix at 6(f F. until the 
dextrose crystals grow to produce a semi- 
fluid plastic (from 3 to 7 days). 

(8) Store under refrigeration. 

Rock i'.nnily 

(1) Use one of the top grades of maple sirup. 

(2) Heat the sirup to SP F. above the boiling 
point of water (67.5= to 70P Brix). 

(3) Store several months at or below room tem- 
perature. 

Hdrd Sugar 

(1) Use any grade of sirup. 

(2) Heat the sirup to between 40P and 45° F. 
above the boiling point of water. 

(3) Remove from the heat and begin stirring 
the hot, thick sirup immediately. 

(4) Continue stirring until ciystals form (sirup 
begins to stiffen). 

(5) Pour the partly crystallized sirup into molds 
to harden. 

Granulated (Stirred) Sugar 

(1) Use a top grade of sirup. 

(2) Heat the sirup to between 4(f to 45? F. 
above the boiling point of water. 

(3) Pour the hot sirup immediately into a tray 
or trough for stirring. 

(4) Begin stirring immediately and continue 
stirring until granulation is completed. 

Miiplc >ni Slum- 

(1) Use the top grades of sirup. 

(2) Heat the sirup to between 22= and 4(r F. 
above the boiling point of water. 

(3) Without stirring, pour the sirup immedi- 
ately onto the snow or ice; it will form a 
glassy, taffylike sheet of candy. 



MAPLE SIRUP PRODUCERS MANUAL 

TESTING MAPLE SIRl P FOR IINVERT SUGAR 



113 



The relation between the invert sugar con- 
tent of maple sirup and its suitability for mak- 
ing maple cream is as follows: 
Invert sugar 
content of 
sirup (percent) Suitability for cream 

0.5 to 2 The right amount of invert sugar 

for making a fine-textured 
cream — one that feels smooth to 
the tongue. 

2 to 4 Can be made into cream if sirup is 

cooked until it is 2° to 4° F. hotter 
than temperature called for in 
standard recipes for cream. 
4 or more Not suitable for cream. If used, su- 
crose will not crystallize, or it will 
crystallize only if sirup is heated 
to a much higher-than-standard 
temperature. Such cream will be 
too fluid and probably will sepa- 
rate a few days after it is made. 

Two tests are available for determining the 
invert sugar content of maple sirup. The simple, 
or short-cut, test merely shows whether the 
sirup contains less than 2 percent of invert 
sugar and is therefore suitable for creaming. 
The other is a quantitative test. It measures 
invert sugar in amounts up to 7 percent, the 
upper limit normally found in maple sirup. 

Simple Test 

The simple test for determining the invert 
sugar content of maple sirup has been adapted 
from a standard test for determining the sugar 
in urine (78, 80). The test is made by first 
preparing a sirup-water mixture (1 part of sirup 
to 20 parts of water) and then color testing the 
diluted sirup. It can be made in 3 or 4 minutes. 

Equipment 

The few pieces of equipment required to 
make the tests can be obtained from the local 
pharmacy. The following items are required: 

(1) Clinitest tablets'" obtainable at pharmacy. 

(2) Two medicine droppers. 

(3) A test tube, about V2 inch in diameter and 

3 or 4 inches long. 



(4) A sample of the sirup to be tested (1 
cupful). 

(5) One medicine glass, calibrated in ounces. 

(6) One glass measuring cup, calibrated in 
ounces. 

(7) Test tube holder. 

(8) Two 8-ounce, clean and dry drinking 
glasses. 

(9) One 1-quart glass fruit jar and cover. 

(10) One "Clinitest" color scale. 

(11) Water (20 fluid ounces). 



M„ki 



tlu- Test 



'" Trademark. This product is one of several that may 
be used by diabetics in testing for sugar in urine. 



(1) Carefully pour enough of the test sirup 
into a medicine glass to bring the level of the 
sirup exactly to the 1-ounce (2 tablespoons) 
mark. If too much (more than 1 ounce) is added, 
empty the sirup out of the medicine glass, wash 
and dry it, and start over. 

(2) Measure 2V2 cups of water and transfer it 
to the quart jar. 

(3) Make the l-to-20 solution by pouring the 
fluid ounce of sirup into the jar containing the 
2V2 cups (20 fluid ounces) of water. 

(4) Pour some of the water-sirup mixture into 
the medicine glass and return it to the jar. 
Repeat this three or four times to be sure that 
all the sirup has been transferred to the water 
in the jar. Mix the contents of the jar thor- 
oughly by stirring with a spoon or with a 
portable electric mixer. 

(5) Place the test tube upright in the holder. 
(The holder can be a 1-inch-thick block of wood, 
2 inches square with a ''/le-inch hole ^/4 inch 
deep.) 

(6) Fill a clean, diy medicine dropper with the 
diluted (1:20) sirup in the fruit jar. Hold the 
dropper upright above the test tube and let 5 
drops of the diluted sirup fall into the test tube. 

(7) Fill another clean and dry medicine drop- 
per with water and add 10 drops of water to the 
test tube. 

(8) Place a Clinitest tablet, freshly removed 
ft'om the bottle or wrapjier, in the test tube. As 
the tablet dissolves, it causes the contents of 
the tube to boil. Do not remove the tube from . 
the holder while the solution is boiling. 



114 



AGRICULTURE HANDBOOK 184, U.S. DEPT. OF AGRICULTURE 



(9) Fifteen seconds after the boiling stops, add 
water to the test tube until it is two-thirds 
filled. 

(10) Observe the color of the solution and 
compare it with the two colors marked + and - 
of the color scale furnished with the Clinitest 
tablets. Disregard everything else on the scale 
card. The other colors and the" labels on the 
scale card have no relation to this test. Make 
the color comparison in a room illuminated with 
an incandescent bulb. The colors are not easily 
judged by fluorescent or direct sunlight. 

Intvritretinfi the Krsiills 

Color of Solution in Test lube. — Blue indi- 
cates a negative test; the sirup contains less 
than 2 percent of invert sugar and can be used 
to make cream. Yellow or yellow gi-een indi- 
cates a positive test; the sirup contains more 
than 3 percent of invert sugar and is not suita- 
ble for making cream. 



Quantitative Test 

The quantitative test is much longer than the 
simple test; it requires about 15 minutes. 

I'rpparing the Siriiit-Wtiter Mixtures 

For this step, you will need sirup, 15 quarts of 
water, measuring cup, quart measure, pail or 
other large container, long-handled spoon, 
small spoon, and five 4-ounce drinking glasses. 
The glasses should be thoroughly dry. You will 
also need a pencil and labels. 

Stir thoroughly the sirup to be tested. Then 
fill the measuring cup exactly to the 1-cup mark 
with sirup. 

Dilute this sirup with five successive addi- 
tions of water, as follows: 

l-and-1'2 Dilutimi (1 cup of sirup and 12 cups 
of water). — Pour 2 measured quarts (8 cups) of 
water into the pail. Pour the cupful of sirup into 
the pail; let the cup drain until most of the 
sirup is out of the cup. 

Measure a third quart (4 cups) of water and 
use this to rinse the remaining sirup from the 
cup; fill the cup with water, stir with a small 
spoon, and pour into the pail until the quart of 
water is used. 

Stir the sirup and water in the pail until it is 
thoroughly mixed. 



Dip one 4-ounce glass into the dilute sirup 
and withdraw half a glassful. 

Label the glass "12" and set it aside. 

l-and-20 Dilution. — To the dilute sirup in the 
pail, add 2 measured quarts (8 cups) of water. 

Stir tlie contents of the pail until well mixed. 
Remove half a glassful and label it "20." 

l-and-32 Dilution. — Add 3 measured quarts 
(12 cups) of water to the mixing pail. Stir 
contents until well mixed. Remove half a glass- 
ful and label it "32." 

l-and-40 Dilution. — Add 2 measured quarts (8 
cups) of water to the pail. Stir contents until 
well mixed. Remove half a glassful and label it 
"40." 

l-and-60 Dilution. — Add 5 measured quarts 
(20 cups) of water to the pail. Stir contents until 
well mixed. Remove half a glassful and label it 
"60." 
Color Tesliiifi the Dihitioiis 

For this step you will need the labeled sam- 
ples of the five dilutions, test tube holder for 
five tubes, five test tubes, six medicine drop- 
pers, Clinitest tablets and color scale, a small 
amount of water, and pencil and paper. 

Make the color test as follows: 

(1) Place five of the test tubes in the test tube 
holder. 

(2) Fill a clean, diy medicine dropper with the 
diluted sirup from the glass labeled "60." Hold 
this dropper upright above the test tube in the 
hole marked "60" and let exactly five drops of 
the diluted sirup fall into the test tube. 

Similarly, place exactly five drops of the "40" 
dilution, five drops of the "32" dilution, five 
drops of the "20" dilution, and five drops of the 
"12" dilution in the tubes numbered for these 
dilutions (see fig. 123). Use a separate, clean, 
dry medicine dropper for each dilution. 

(.3) Fill another clean medicine dropper with 
water and add 10 drops of water to each of the 
five test tubes, refilling the medicine dropi^er as 
necessary. 

(4) Remove five Clinitest tablets from the 
bottle or wrapper. Place them on a clean piece 
of paper. 

(5) Place one tablet in each test tube, in order, 
starting with the tube marked "60." 

The tablets, as they dissolve, cause the con- 
tents of the tubes to boil. Do not move the test 
tubes while tlie solutions are boiling. 



MAPLE SIRUP PRODUCERS MANUAL 



115 




Figure 123. 



PN-1S19 
-Testing sirup for invert sugar. 



Write down in order the values you have 
griven the five dilutions, starting with the 1-and- 
12 dilution at the left. 

Special Note. — If the first sirup you test 
proves positive in some dilutions and negative 
in others, you will quickly see the difference 
between a positive and a negative color reac- 
tion. 

It is possible, however, that the sirup you test 
will give a positive or a negative test in all 
dilutions. If this happens and you ai'e doubtful 
about your interpretation of the results, it will 
be helpful to have a solution that you know will 
give a jx)sitive test. 

To prepare such a solution, add three drops of 
corn sirup to the 4-ounce glass containing the 
sample of the l-and-60 dilution. Stir the com 
sirup into the dilute sirup. 

In a clean test tube place five drops of this 
solution. Add 10 drops of water, then one Clini- 
test tablet. After boiling has stopped add water 
until the test tube is two-thirds full. 

The color that develops will indicate a posi- 
tive reaction. 



(6) Fifteen seconds after the boiling stops, add 
water to the test tube marked "60" imtil the 
tube is two-thirds full. Add the same amount of 
water to the other four test tubes, in order, 
from right to left. 

(7) Compare the colors in the test tubes with 
the two colors of the color scale marked "trace" 
and "-f^". Disregard everything else on the 
scale; the other colors and the labels on all the 
colors have no relation to this test. 

Make this comparison in a room lighted with 
an incandescent bulb. You cannot judge the 
colors of the solutions for this test with fluores- 
cent light or with sunlight only. 

Assign to the mixture in each tube one of 
three values — positive (+ ) for invert sugar, neg- 
ative (-) for invert sugar, or doubtful (±) ac- 
cording to the following standard: 



Color of solution Value 

Same as or more blue than color on scale 

labeled "trace" Negative (-) 

Same as or more yellow than color on 

scale labeled " + " Positive ( + ) 

Between "trace" and " + " colors on scale Doubtful (± ) 



Detorniiiiiiig In>ei't Siiftar Content of 
Sirup 

To find the invert sugar content of the sirup 
you are testing, find the line in table 17 that 
contains the same combination of values for the 
five dilutions that you obtained in the color 
test. 

As the table shows, the sirups that are most 
suitable for making into cream are those that 
are negative in all dilutions or positive in the 
first (l-and-12) dilution and negative in all the 
others. 

Suniniaiy 

(1) Test the sirup for its invert sugar content 
before attempting to make maple cream. 

(2) Use the simple or shortcut test, page 113. 

(3) To check the color, positive or negative, use 
a test .solution consisting of the 1- and 60- 
solution to which is added com sirup, page 
115. This will give a positive test. 

(4) Sirup containing more than 3 percent of 
invert sugar is unsuitable for creaming. 



116 



AGRICULTURE HANDBOOK l.'?4. U.S. DEPT. OF AGRICULTURE 



Table 17. — Key for interpretinx) results of color test for invert siigar content of five dilutions of 

maple sirup 



[- indicates negative reaction; + indicates positive reaction; ♦ indicates doiibtlul reaction! 



Reactions for 5 test dilutions 



Invert-sugar content of sirup 



Suitability of sirup for making into 
cream 



Percent 

Less than 2 Suitable. 

More than 2, less than 3 Suitable. 

More than 2, less than 4 Suitable if sirup is heated 2 to 4 

degrees higher than usual in cream- 
making. 

More than 3, less than 4 Not suitable. 

More than 3, less than 5 Not suitable. 

More than 4, less than 5 Not suitable. 

More than 4, less than 6 Not suitable. 

More than 5, less than 6 Not suitable. 

More than 5, less than 7 Not suitable. 

Above 6, may be 7 or more Not suitable. 



THE CErNTRAL EVAPORATOR I'LAINT 



Before 1955 no market existed for maple sap. 
The sap crop had to be converted to sirup or 
some other product on the farm where it was 
produced before it became marketable. Maple 
sap, therefore, occupied a unique position in 
American agriculture because all other farm 
crops are marketable as produced. 

This practice contributed little toward devel- 
oping the maple industry or toward moderniz- 
ing sap production to make it competitive with 
dairying, stock raising, or gi-ain farming. 

The cuiTent trend toward central evaporator 
plants (figs. 124 and 125) has marked a new era 
in the maple industry. No longer do all sap 
producers have to be skilled sirupmakers; in- 
stead, the central plants are operated by and 
staffed with specialists not only in sirupmaking 
but also in marketing. Other advantages of- 
fered by the central evaporator plants are: 

(1) The central plant eliminates the former 
duplication on each farm of invested capital for 
evaporator and related equipment and for an 
evaporator house. 

(2) The farm plant often was too small to be 
operated economically and was wasteful of la- 
bor. A small evaporator having an output ca- 



pacity of 1 to 5 gallons of sirup per hour re- 
quires as many man-hours for its operation as 
does the central evaporator plant that produces 
15 or more gallons of sirup per hour. 

(3) Thousands of farmers with stands of ma- 
ple trees that they had not previously used for 
sap-sirup production now find it practical and 
economical to produce and sell a sap crop. 

(4) A more uniform and better quality prod- 
uct can be produced in a central plant. This 
tends to stabilize the market. 




PN-1S20 

Figure liJ,. — This central evaporator plant at Ogema, 
Wis., has one evaporator. 



MAPLE SIRUP PRODUCERS MANUAL 



117 




Figure 125. — A large central evaporator plant located at 
Anawa, Wis. Some plants are large enough to make 20 
or more gallons of sirup per hour. 



L«>4-atioii 

The site for a central plant should be cai-e- 
fully chosen. Some of the factors to be consid- 
ered are: 

(1) It should be centrally located in relation to 
the sap-producing farms. 

(2) It should be on an improved road, prefera- 
bly at an intersection. The road should bear 
considerable nonlocal traffic. 

(3) It should have adequate space for drive- 
ways for delivery of sap. 

(4) It should have an access roadway from the 
main road and off-road parking areas for visi- 
tors (customers). 

Size 

Like other industries, the size of the central 
evaporator plant will be governed by a number 
of factors that can readily be determined. Un- 
like other industries, the central plant can eas- 
ily be expanded to accommodate increased de- 
mands because of the relative simplicity of 
equipment and plant design. 

The initial plant must be large enough so 
that the volume of sirup produced will yield 
reasonable returns on the invested capital and 
so that labor will be used economically. These 
two factors will be determined by the cost of the 
sap, the number of hours per day the plant is 
operated and the length of the season, the 



number of man-hours required to operate the 
plant, the output, and the price of the finished 
product. These factors, in turn, depend on the 
size of the evajwrators, the density f Brix) of 
the sap, and the efficiency of the plant. 

Since the plant handles liquids (sap and sir- 
up), it can be completely automated. The extent 
of automation will be governed by the size of 
the i)lant and the budget. The cost of producing 
a gallon of sirup decreases as plant size in- 
creases. 

An evaporator plant building of shed roof 
design permits easy expansion. The shed roof 
building can be doubled in size by adding three 
walls to convert it to a gabled roof building. The 
building must be large enough to permit easy 
access to the evaporators and other equipment. 
The materials should be easy to clean, such as 
concrete floors, smooth walls, and built-in cup- 
boards and resti-ooms. Provision should be 
made for a candy kitchen and a salesroom. 

The most common type of central evaporator 
plant uses oil heat to evaporate the sap in tlue 
pans, each of which is independently installed 
on its own arch with its own oil burner (see p. 
59). A coil or tube of high-pressure steam is 
used to heat the finishing pan, which is also 
mounted on its own support (fig. 126 and chart 
23). 




PN-1822 

Figure 126. — Interior of a modern central evaporator 
plant at Bainbridge, N.Y. Oil heat is used to evaporate 
the sap in the four flue pans and high-pressure steam 
is used at the finishing stage. 



118 



AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE 



CENTRAL SAP EVAPORATOR PLANT 





Chart 23. — Flow diagram: Oil-and-steani plant. 

Coal is used in some areas, particularly 
where it is cheap. It is best used to generate 
high-pressure steam which, in turn, is used to 
evaporate the sap (fig. 127). 

As with oil-fired evaporators, a series of pans 
is used. These pans, like the oil-fii-ed pans, are 
mounted stepwise, as shown in figure 128. The 
pans are heated with 80 to 110 p.s.i.g. steam in 
coils or manifolds of ^/4-inch brass tubing 
mounted at the bottom of the flat pans. 

The specifications for a small plant (about 
8,800 gal. per season) described by Pasto and 
Taylor {86) are as follows: 



Sap gallons per hour. 

Water evaporated do 

Sirup produced do 

Tapholes number.,. 

Fuel consumption gallons 

Capital investment dollars. _. 

Floorspace square feet 

Sap storage gallons... 



Density of 


sap at — 


1.6° 


2.4° 


Brix 


Brix 


807 


815 


792 


792 


14.7 


22.2 


32,000 


32,000 


23,800 


23,800 


25,291 


25,291 


1,226 


1,226 


20,000 


20,000 



Capital investment and cost for depreciation 
and repairs for a small plant, as reported by 
Pasto and Taylor {86), are given in table 18. 

Smaller plants are in operation and are prov- 
ing highly successful. Usually these plants are 
small initially, but they are built so that they 
can be enlarged after 2 or 3 years' operation. 
Typical of these is the central evaporator plant 
established in 1962 at Ogema, Wis. (fig. 124). 
This plant has one 6- x 20-foot evaporator and a 
separate finishing pan. Sap is supplied from 
9,500 tapholes on 16 farms. 

Operation 

The sap supplied to the evaporator from the 
storage tanks is fed to the first flue pan. Since 
the flue pans are connected in series, the sap 
flows successively through each pan to the 
next. The sap is conducted between pans 
through large-diameter, heat-resistant tubes or 
pipe at least IV2 inches in diameter. The pans 
can be installed in a stepwise manner to insure 
no backward flow of sap from pans of higher 
concentration to pans of lower concentration 
and to better control the depth of the liquid 
level in each pan. Since the elevation between 
pans is only 6 to 8 inches, there is only a small 
hydrostatic pressure in each interconnecting 
feed line. Feed lines and valves must be large 
enough to supply sap to the pans rapidly 
enough under this low pressure to replace the 
vast quantities of water being removed by 
evaporation. 

The liquid level in the evaporator pans is 
maintained at a fixed depth by means of a 
mechanical float valve or by an electrically 
operated liquid level sensing element and sole- 
noid valve. Whichever mechanism is used, it 
must be sensitive to minute changes in liquid 
level and must operate instantaneously. In 
principle, when the finishing pan requires more 
liquid to maintain its depth of sap, the sap is 
obtained from the third pan of a 3-flue pan 
installation, which in turn obtains more sap 
from the second pan, and so on back to the 
storage tank. The sirup is removed from the 
finishing pan when it reaches standard density 
(66.(f Brix) or slightly higher. 

The operation can be automated by use of a 
thermoswitch and solenoid valve. The thermo- 
switch is adjusted to open the valve when the 



MAPLE SIRUP PRODUCERS MANUAL 



119 



boiling sirup reaches the desired temperature 
above that for boiling water at that location. 
The operation is not completely automatic, 
since the thermoswitch must be handset as 




PN-)K23 

Figure 127.— Where coal is inexpensive, high-pressure 
steam boilers may be used to evaporate sap to sirup. 




PN-4824 

Figure i2^. — Interior of a multiple-pan, all-steam central 
evaporator plant at Stoystown, Pa. 



many as three or four times a day to compen- 
sate for fluctuations in barometric pressure. 
The U.S. Department of Agriculture has devel- 
oped a new controller that will automatically 
compensate for changes in the boiling point of 
water due to changes in barometric pressure 
(15). 

In some installations, the partly concentrated 
sirup is not supplied to the finishing pan by 
gravity feed. Instead, an electric pump, acti- 
vated by an electrically operated liquid level 
sensing device in the finishing pan, removes the 
sap from the last flue pan or semifinishing pan 
when it reaches the desired concentration — any 
point between 2(f and 60? Brbc. 

If the Brix value of the sirup supplied to the 
finishing pan is above 5(f , essentially all of the 
sugar sand will have been formed and will be in 
suspension. Its viscosity will be very low (see 
table 13). It is advantageously filtered at this 
point. The filtered sirup is then pumped into 
the finishing pan. When it reaches the desired 
density, it is automatically drawn by means of 
solenoid valves and thermoswitch, and piped to 
the holding or canning supply tank. With this 
procedure, little or no sugar sand is formed in 
the finishing pan. A cartridge-type filter can be 
installed in this line to iwlish the sirup (that is, 
remove the cloudlike precipitated sugar sand). 
If the sirup is not prefiltered, it can be piped 
from the finishing pan to a pressure filter such 
as a plate-and-frame type and then to the 
holding tank. Either method is desirable, since 
once the sirup reaches standard density, it is 
kept in a closed system so that it cannot evapo- 
rate further. 

To reduce holdup time, it is good practice to 
keep the liquid level as low as possible in each 
evaporator. There is, of course, always a danger 
that because of some failure, insufficient liquid 
will be fed to each pan and the pan will be 
ruined by burning. This can be prevented by 
connecting a hose to the raw-sap feed line by 
which sap can be added quickly to any location 
in any one of the pans. 

Although a gas-fired finishing pan is satisfac- 
tory for smaller plants, it is advisable to use 
high-pressure steam for the finishing pan in 
plants that make as much as 15 gallons of sirup 
per hour. The steam permits finishing the sirup 
without danger of burning it. The steam is best 



120 



AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE 



supplied from an automatically operated, liijjh- 
pressui-e boiler (80 to 110 p.s.i. and a rated horse- 
I)ower of 20 or more). 

If no prefilti'ation or inline cartridg:e filters 
are used, the finished sirup can be efficiently 
and economically filtered immediately after it is 
drawn from the evaporator. A battery of three 
or more open, flat, felt filtei's stsould be used. 



Allowance must be made for loss of water as 
steam while the sirup is being filtered. This loss 
tends to raise the Brix value of the sirup 
approximately Y . 

S;i|> .S|||»|>|i4-|-s 

Sap can be obtained in any one of three ways: 
(1) It can be obtained from rented trees; (2) it 



Table 18. — Capital investment in plant and equipment and cost of depreciation and repairs for 

small oil-and-steam type plant ' 



Life 
length 



Yearly 
depreciation 



Yearly 
repairs 



Dollars 

Land (1 acre at $200) 200.00 

Roadway, ramps, grading 

Building (1,226 sq. ft. at $4 per sq. ft.) 

Equipment and other items: 

Sap-receiving tanks (19,495 gal. at $0.08,3 per gal.) 

Germicidal lamps for sap receiving tanks (12 at $25) 

Pump for sap 

Sap filter 

Flue-type sap evaporators (4 at $650) 

Arches for sap evaporators (4 at $287) 

Covers and stacks for sap evaporators (4 at $160) 

Steam semifinishing evaporator, size 5 x 6 ft 

Cover and stack for semifinishing evaporator 

Steam finishing evaporators and coils (2 at $100) 

Hoods and stacks for finishing evaporators 

Float valves (5 at $5) 

Oil burners (4 at $332) 

Smokestacks (4 base stacks at $31; 4 top stacks at $57) 

Finishing filter (2 at $14.70) pressure cartridge 

Finished sirup holding tank with heating device 

Finshed sirup storage tank (3,940 gal. at $0.25 per gal.) __ 

Steam boiler (20 h.p.), installed 

Oil tank (8,000 gal.) 

Automatic sirup drawoff 

Gravity filter 

Pumps and motors to filter and to finishing evaporators (2 

units at $75) 

Can filling equipment 

Thermometers (2 at $50) 

Testing equipment ( re fracto meter, $100; hydrometer, $48; 

scales, $150; thermometers, $10) 

Portable power-stirring device 

Water supply (well) plumbing, sink 

Restroom furnishings 

Office equipment 

Other installation charges (burners, tanks, pumps, etc., 

besides cost of equipment) 

Miscellaneous 

Total 

' About 8,800 gal. per year. 1962 dollars. 
Source: Pasto and Taylor («6). 



Dollars 



500.00 


20 


22.50 


15.00 


4,904.00 


30 


147.12 


147.12 


1,618.08 


20 


72.81 


48.54 


300.00 


10 


27.00 


9.00 


150.00 


10 


13.50 


4.50 


50.00 


10 


4.50 


1.50 


2.600.00 


10 


189.00 


63.00 


1,148.00 


10 


103.32 


34.44 


640.00 


10 


57.60 


19.20 


138.00 


10 


12.42 


4.14 


108.00 


10 


9.72 


3.24 


200.00 


10 


18.00 


6.00 


100.00 


10 


9.00 


3.00 


25.00 


10 


2.25 


.75 


1,328.00 


10 


119.52 


39.84 


352.00 


10 


31.68 


10.56 


29.40 


10 


2.29 


.76 


75.00 


10 


6.75 


2.25 


985.00 


20 


44.32 


29.55 


4,485.00 


20 


201.83 


134.55 


1,000.00 


20 


45.00 


30.00 


100.00 


10 


9.00 


3.00 


140.00 


10 


12.60 


4.20 


150.00 


10 


13.50 


4.50 


50.00 


10 


4.50 


1.50 


100.00 


10 


9.00 


3.00 


308.00 


10 


27.72 


9.24 


300.00 


10 


27.00 


9.00 


1,000.00 


20 


45.00 


30.00 


500.00 


30 


15.00 


15.00 


500.00 


10 


45.00 


15.00 


912.00 


10 


82.08 


27.36 


800.00 


10 


72.00 


24.00 


25.791.48 




1,502.,53 


7.52.74 



MAPLE SIRUP PRODUCERS MANUAL 



121 



can be picked up at the farm; or (3) it can be 
delivered to the plant (figs. 129 and 130). 

The quality of sap is not easy to judge by 
visual inspection. But the buyer must guard 
against purchasing spoiled or unsound sap, 
since a small amount could contaminate a large 
amount of sound sap when added to it. The 
plant operator must therefore exercise some 
control over the production of sap by the sap 
suppliers. He therefore should set certain mini- 
mum standards. 

I'rotliirtioii Stdmlards for Sa/t I'.ollevted in 
Buckets 

(1) All buckets must be covered. 

(2) Buckets must be clean and sanitized be- 
fore use. 

(3) In midseason or after a warm period, 
buckets must be washed again. 

(4) Collecting buckets and tanks must be kept 
clean and sanitized. 

(5) Sap (even a very small amount) that has 
remained in buckets between runs must be 
discarded. 

Production Standards for Sfip Collected in 
Plastic Tubinfi 

(1) Only clean tubing must be installed. 

(2) All collecting or venting equipment must 
be washed and sanitized. 

Standards for Slorti^e Tanks on Sti/t harms 

(1) All tanks must be washed and sanitized 
before the start of the sap season. 

(2) Tanks must be completely emptied, 
washed, and sanitized at least twice each sea- 
son and preferably between each run of sap. 





PN-ia2.s 
Figure 129. — Sap i.'i delivered to a central evaporator 
plant in a variety of vehicles. These vehicles are waiting; 
to unload. 



PN-4826 

Figure 130. — Sap is delivered in all types of containers 
(including- milk cans) and by eveiy available type of 
conveyance ranging from the trunks of passenger cars 
to trailers drawn by farm tractors. 

Pi-oduction of a darker grade of sirup indicates 
that the tank needs washing and sanitizing. 

(3) Tanks should be covered with clear, trans- 
parent plastic that transmits the sanitizing 
ultraviolet radiation of sunlight. 

(4) Tanks must be constructed with smooth, 
easily cleaned surfaces. 

Metal tanks best meet the requirements. 

l*iirohafi«' of Sap 

Sap is bought on the basis of the total weight 
of solids (sugar) it contains. It is necessary to 
measure with precision the volume of the sap to 
the nearest gallon, its density to the nearest 
0.1° Brix, and its temperature to the nearest ° F. 

The volume of sap can be determined in 
several ways, as follows: 

(1) By means of a meter through which the 
sap can be pumped or can flow by gravity. This 
is the most precise and direct method, provided 
the meter is calibrated carefully and is checked 
frequently. Be sure the meter is designed for 
operation at low pressures. 



122 



AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE 



(2) By use of tanks of standard sizes cali- 
brated in gallons for different depths of liquid. 
The calibrations are usually made on a "dip 
stick" calibrated for a specific tank size. The 
stick is lowered vertically to the bottom of the 
tank and the heipfht of the sap in the tank is 
noted by the wet line on the stick. This line 
indicates the depth and volurne of the sap. 
Usually, when sap is delivered to the plant, it is 
run into a receiving tank that can be calibrated 
precisely. The calibrations should be accurate 
to ± 1 gallon. 

(3) By its weight. The tank of sap is weighed 
before and after emptying. The empty (tare) 
weight is subtracted from the weight of the 
tank and sap to obtain the weight of sap. The 
weight of sap is divided by 8.39 (the weight of 1 
gallon of sap). 

The only tangible constituent of sap that can 
be used to establish its price is its solids con- 
tent, which is measured and expressed as 
° Brix. This measurement is made at the plant 
by using a quart sample taken when the sap 
was picked up at the farm or when it was 
delivered to the central plant (fig. 131). The 
sample identified with supplier's name and date 
can be stored a few hours before determining 
its Brix value. Or its Brix value can be deter- 
mined at the time the sap is picked up or 
delivered provided its temperature is also deter- 
mined at that time. 

The observed Brix value of the sap is the 
value read to the nearest 0.1° from the test 
instrument (hydrometer or refractometer); this 
value, together with the measured temperature 
of the sap, is recorded. From these, the true 
Brix value of the sap is calculated. 

Corrections to be applied to the observed Brix 
value to obtain the true Brix value of saps of 
various temperatures are as follows: 



Temperature of sap, ° F. 

32-42 

43-53 

54-62 

63-66 



Correction to subtract from 
observed Brix value 

CBrix) 

0.4 

.3 

.2 

.1 



The value of sap is not constant but varies 
with its solids content (percentage of sugar), or 
Brix value. The higher the Brix value, the 
smaller the amount of sap required to produce 



1 gallon of sirup. Less water has to be evapo- 
rated, less volume is handled, and less storage 
space is required. Sap with the highest Brix 
reading therefore has the highest value. 

The base price for sap is usually for sap of 2" 
Brix. This base price is determined by a num- 
ber of factors, the most important of which is 
the price of the finished sirup. For sirup selling 
at $9 to $12 a gallon, one New York producer 
reported in the National Maple Syi-up Digest (1) 
the following prices paid for sap delivered at 
the evaporator plant in 1974. The prices can be 
adjusted up or down by such factors as effi- 
ciency of the plant, hours of operation, and 
wage scales. 

True Brix value of sap ' 



1.5° 
1.6° 
1.7° 
1.8° 
1.9° 
2.0° 
2.1° 
2.2° 
2.3° 
2.4° 
2.5° 
2.6° 
2.7° 
2.8° 
2.9° 
3.0° 
3.1° 
3.2° 
3.3° 
3.4° 
3.5° 
3.6° 

3.r 

3.8° 
3.9° 

4.0° 



Price per gallon 
(cents) 

2.9 

3.9 

4.9 

5.8 

6.6 

7.3 

7.9 

8.5 

9.1 

9.7 

10.2 

10.7 

11.2 

11.7 

12.2 

12.7 

13.2 

13.7 

14.2 

14.7 

15.2 

15.7 

16.2 

16.7 

17.2 

17.7 



' True Brix value is the observed Brix reading corrected 
for temperature. 

Storing Sap 

The central evaporator plant must provide 
facilities to store a full day's production of sap. 
There is no precise means for estimating the 
size. However, experience has shown that on 
days when sap flows well, ft'om 4,000 to 20,000 
gallons will be produced per 10,000 tapholes. 
Thus, a plant having a capacity of 8,800 gallons 



MAPLE SIRUP PRODUCERS MANUAL 



123 




PN-4827 

Figure 131. — A sample of sap is taken for determining its 
Brix value and for judging its quality. The observed 
Brix value, temperature, and volume of the sap are 
recorded for each delivery. 

of sirup annually would I'equire sap from 10,000 
to 35,000 tapholes, or 70,000 gallons of sap per 
day. Since the plant would be operating contin- 
uously after the first delivery of sap, the re- 
quired storage facilities would be somewhat 
less than the daily requirement of sap. 

Storage tanks can be made of several mate- 
rials and in several shapes. Metal-lined tanks 
are preferred because their surfaces are 
smooth, easily cleaned, and sanitary. Concrete 
tanks are the most difficult to keep clean be- 
cause droplets of sap, in which micro-organisms 
can gi'ow, can lodge in the rough surfaces. 
Concrete walls can be made smooth with differ- 
ent types of coatings; however, before the walls 
are coated, clearance for the use of the particu- 
lar coating should be obtained from State and 
Federal food agencies. Plastic tank liners also 
have been used successfully, especially in 
wooden tanks. 



The storage tanks should be located in a cool 
place. Aboveground storage is preferable be- 
cause of ease in making repairs and cleaning. 
All tanks must be covered- If the tanks are not 
equipped with germicidal lamps, they should 
have transparent plastic covers and should be 
located to receive as much sunlight as |X)ssible. 

Because of the depth of the sap in the tanks, 
the efficiency of daylight sterilization is low. It 
is recommended that germicidal lamps be used. 
One or more lamps should be arranged to illu- 
minate the entire surface of the sap. The lamp 
fixture should be provided with a bright metal 
reflector so that most of the ultraviolet radia- 
tion will be used. These lamps are also effective 
in sanitizing empty or partly empty tanks, pro- 
vided no buildup of foam or solids has occurred 
on the tank walls. 







CAUTION 










(!aro nmst 


he 


(■x<'r<'is«M 


not to 


.■X 


>OM- 


tlio < 


vcs lo 


•Uro 


<•! iiltra\iolc 


1 ra< 


lial 


ion. 


.4lHa\ 


•> turn 


he 1 


amps olT 


vth< 


•11 th 


■ 1; 


inks 


ai-e <• 


t-aiicd or \^ 


lien ihcv 


art' 


opciic* 


lor 


»'iil<'i 


iii^ <>r 


for 


iiis|M-cli<>ii. 


riti 


a\ioh-t 1 


rays. 


<-an «!<> 


irr< 


parahlr 


(hiiiiag)' 


lo 


Ih.- 


evt's. 

















The receiving tank (fig. 132) should be placed 
alongside a ramp so that the sap in the hauling 
tanks can be emptied into it by gravity. In some 
localities it is possible to have the receiving 
tanks installed higher than the storage tanks 
so that they also can be filled by gravity. 




Figure 132. — The sap is filtered as it 
receiving tank. 



PN-4828 



is run into the 



124 



AGRICULTURE HANDBOOK 184, U.S. DEPT. OF AGRICULTURE 



However, the more common method is to move 
sap from the receiving: tanks to the storage 
tanks by i)iimi)s. 

Sap obtained from pijDelines is usually free of 
foreign matter and does not need to be filtered. 
However, sap obtained by other collecting 
methods must be filtered to remove fine parti- 
cles of bark and other foreign matter from the 
sap. If not removed, this foreign matter may 
serve as an unwanted source of color and cause 
the production of dark, low-gi-ade sirup.- The 
filter may be either a presscloth prefilter or 
several thicknesses of muslin (fig. 133). 

It is desirable to use two or more sap-storage 
tanks. This permits better control of sanitation, 
plant operation, and production records. The 
Brix value of the sap in each tank must be 
determined since it may be a composite of sap 
obtained from two or more sources that may be 
of different sugar contents. If the volume of sap 
in the tank and its Brix value are known, the 
yield of finished sirup can be calculated (see p. 
48). 

The evaporator house must be provided with 
a gage to show the volume of sap in the storage 
tank being used to supply sap to the evapora- 
tor. Without a gage, the plant operator may 
unexpectedly find the supply of sap exhausted, 
and the evaporator pans may go diy and be 
damaged by bm-ning. A simple type of gage can 
be installed in the sap feed line from the tank to 




PN-1H29 

Figure 133. — Several layers of muslin or presscloth can be 
used to filter sap. 



the evaporator This gage consists of a tee with 
a long, upright, glass sight tube, the top of 
which is open and above the level of the top of 
the storage tank. The level of the sap in the 
tube indicates its depth in the storage tank. 
The tube can be calibrated in units such as full, 
'/.,-full, etc., or in gallons. 



Handling und Storing Sirup 

Sirup tends to become darker each time it is 
heated above 18(F F. Therefore, sirup should be 
reheated as few times as possible. To insure a 
sterile package, all sirup must be packaged at 
temperatures above 19(F. It is advisable to 
package the sirup immediately after it leaves 
the filter or the finishing pan while it is still 
above 190^. If the temperature of the sirup 
drops below 19(]F before it can be packaged, a 
small amount of heat furnished by a steam coil 
with high-pressure steam, an electric immer- 
sion heater, or a heat lamp will bring it back to 
the desired 19(7 with a minimum of darkening. 

Sirup not immediately packaged can be put 
in bulk storage. If it is stored in drums, they 
must be completely filled with hot sirup 
(19(F F.). Large tanks holding several hundred 
or several thousand gallons can be used. Sirup 
storage tanks, like sap storage tanks, should be 
provided with germicidal lamps mounted to 
illuminate the entire surface of the sirup when 
the tank is filled. These lamps must be kept in 
operation continuously from the time the tanks 
are cleaned prior to filling until the last of the 
stored sirup has been removed. If the sirup is 
run into these tanks hot and sterile, there is 
little chance that any microbial gi'owth will 
occur below the sirup surface, and the germici- 
dal lamps will keep the surface sterile. Sirup 
stored in this way can be held indefinitely and 
sirup can be added or withdrawn at any time. It 
is not necessary to keep the tank cool. Tanks 
with sterile lamps can be mounted outside, for 
the ambient temperature has little or no effect 
on keeping quality of the sirup. The sirup with- 
drawn for packaging must be heated to sirup- 
pasteurizing temperature (190" F.). 

The large storage tank also serves as a set- 
tling tank. After several weeks of storage, the 
sirup will be sparkling clear. 



MAPLE SIRUP PRODUCERS MANUAL 125 

SailitUtioil ^- Labor (supervisor plus hourly wages at 

$1.50 per hour) 1,255 

The central evaporatinfj plant is a fond proc- 

essing: plant. It must be maintained in the same Total ' 

clean and sanitary manner that is required of . „ ^ . , , 

..„,." F. Income (8,800 gallons of sirup produced; 

all food plants. price received per gallon, $4.3,'ir 38.104 

The evaporator room and any other rooms m Net profit, F - (B + c+D + E), or $38,i04 - 

the plant should be kept free of steam. Moist $28,211 9,893 

surfaces are sites for microbial growth. Steam Return on capital investment: 

is easily removed from the evaporators by us- ^ jqq ^ ^g percent " 

ing the closed venting system described on page $25,291 
40. 

The floors should be constructed of smooth ' Except for average price per gallon of sirup, these 

. r 1 • data are adapted from Pasto and Taylor (86). 

masonry for ease of cleaning. , g^^ ^^^1^ jg j.^^ itemized capital expenditure. 

The sirup should be packaged in a separate :< p^^ed costs, with the possible exception of salaries 

room or area that can be kept clean and free of paid to management, remain constant irrespective of 

dust. Clean all equipment at frequent intervals. production. 

When detergents and scale-removing chemicals ] Cost of sap. This depends on two variables: (i) The 

, . , , i 1 J u volume of sap processed, and (2) the Brix (percent oi 

are used, they must be completely removed by ^^,g^^, ^^ ^^^ ^^p ^^^^ ^^^ ^^^^ ^^^^^^ p^^^ p^i^ f^,. ^^p 

at least three successive rinses with clean, clear ^f 2.4° Brix in 1963. 

water. ' The price received for a gallon of sirup is based on an 

Only clean utensils should be used and in- assumption that '/:, will be sold in bulk at $3 per gallon, 'A, 

Struments should be kept free of sugar sand. at a bulk price of $4, and V., sold retail at $6 per gallon. 

Return on capital for sirup at the plant; does not 
include marketing costs. 

Economics 

^, , , , • ■ -1 r The previous data assume maximum produc- 

The central evaporator plant is primarily tor . ,. n i ^ t ^ t-- i^ 

^ . , r. r, ■ I tion tor a small plant. Less production would 

concentrating sap to sirup and tor iiltering and , <.<■•* j • e ■ <- ^ 

r „ , ^ XI • -^ -11 u reduce net profit and income from invested 

packaging sirup. When used tor this, it will be . , 

operated only 6 to 8 weeks a year. Yet even 
with this short period of use, Pasto and Taylor 

(86) found in 1962 that such a plant could pay Material lialaun' 

an excellent return on the invested capital. The Seldom will the actual amount of sirup pro- 
following calculations, based on Pasto and Tay- duced equal that calculated from the amount of 
lor's data, show how profitable such an opera- gap purchased and the Brix value of the sap. 
tion could have been at that time. By recalcu- Pasto and Taylor (86) suggested that there is a 
lating, using current costs and prices, one could 2-percent loss in sirup. They suggested that this 
determine whether the return to be expected is due to sirup left sticking to the walls of the 
would be higher or lower than that shown here. evaporators, holding tanks, and felt filters. This 

apparent loss is caused (1) by making sirup that 

Returns on capitalinvestment in small central evaporator is too heavy (a Brix value above 66.(f), and 

plant used only for processing sap and filtering and selling this heavy sirup on a volume basis 

packaging sirup ' rather than on a weight basis; (2) by overfilling 

. , X i , . . . . cSc Of,, sirup containers; as little as 5-percent overfill in 

A. Investment in plant and equipment ■ $25,291 •, , , ■ , 

the retail package results in only 950 gallons oi 

Costs (operating): sirup for each LOGO gallons handled — a loss of 

B. Fixed (management, interest on borrowed 50 gallons; and (3) by removing during filtration 

capital, depreciation, repairs, insurance, sugar sand that was measured in sap as sugar. 

property taxes)' 6,277 ^p^^ longer the plant is in productive opera- 

Variable: " 

C. Sap supplies (322,292 gal. (2.4° Brix) at tion (hours and days) and the greater the vol- 

$0,052 per gal.)^ 16,7.59 ume of sirup produced, the greater will be the 

D. Fuel (26,136 gal. oil at $0.15) 3,920 profits and returns on the investment. 



126 



AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE 



I iH-rcasinf! Returns 

Use of central plant facilities need not be 
limited to the 6 or 8 weeks of sap evafwration. 
Instead, the facilities can be put to a number of 
other uses that not only produce more income 
from the invested capital but also furnish prof- 
itable employment. 

Additional uses for the plant~are: (1) Mixing 
of sirups to obtain a standard grade and den- 
sity; (2) custom packaging of sirup; (3) prepar- 
ing gift packages; (4) reprocessing sirup to re- 
move buddy flavor; (5) making high-flavor sir- 
up; (6) preparing high-density sirup; and (7) 
manufacturing confections. 

Some additional equipment would be re- 
quired. This includes a steam kettle for use in 
processing sirup and in manufacturing confec- 
tions and a candy machine and facilities for 
manufacturing confections. 

Standardizing Sirup for Color 
and Density 

Today, the consumer exjjects uniformity in 
food products. The public, therefore, expects 
uniformity (year after year) in the color (gi-ade) 
and density of maple sirup. The color and den- 
sity can easily be adjusted to meet specific 
customer demands by mixing sirup of different 
grades and different densities. This must be 
done after the sirupmaking season so that the 
amount of different sirup stocks will be known. 

Adjiisliiif: Color 

To adjust the color, measure 1 cup of either 
the lighter sirup or the darker sirup in a 2-cup 
measurer. Then add the other with constant 
mixing until the desired color (grade) is 
reached. Note the amount of sirup added in 
ounces. This will give the ratio of the light and 
dark sirups to be mixed to produce the desired 
grade. 

Stirring sirup in .5-gallon tins makes it easier 
to select different gi-ades for mixing. 

Adjiisling Ih'iisilY 

To adjust the density, preferably to between 
66^ and 67° Brix, the method of Pearson's 
Square can be used. Considerable time can be 
saved by calculating the number of parts (by 
weight) of the heavy sirup to mix with sap or 
thin sirup to obtain standard-density sirup. 



Example 1. If a dense sirup of 70^ Brix is to be 
mixed with a thin sirup of 64.4' Brix to make a 
standard-density sirup of 66.0^ Brix, the quan- 
tity of each sirup to be used can be determined 
by alligation as follows: 



A = 70 



D = 1.6 (calculated) 



C = 66.0 



B = 64.4 



4.0 (calculated) 



where A = density of heavy sirup in ° Brix 
B = density of light sirup in ° Brix 
C = density desired as the result of mix- 
ing A and B 

This is always the center figure. D = the 
difference between C and B, which in this case 
= 1.6. E = the difference between A and C, 
which in this case = 4.0. D and E give the ratios 
of sirup A and B to mix to produce standard- 
density sirup (66.0P Brix), which in this case 
would be 1.6 parts of A (heavy sirup) to 4.0 
parts of B (light sirup). 

Example 2. If sirup with a density of 66.5^ 
Brix is desired (it will feel better to the tongue) 
using the same two sirups, the Pearson Square 
would become 



70 



D = 2.1 



C = 66.5 



B = 64.4 



E = 3.5 



The ratio of these two sirups mixed to give a 
sirup having a density of 66.5" Brix (C) would be 
2.1 parts of A (hea\y sirup) to 3.5 parts of B 

(light sirup). 

rii<<loiii l'a<-kafiiiiji and (.ill l'a«'ka}>;«'.s 

Many customers want sirup packaged in con- 
tainers of special design and shape. This re- 
quires special handling, and is usually done 
after the. sap season. 



MAPLE SIRUP PRODUCERS MANUAL 



127 



Many companies and some individuals are 
using gift packages for a selected clientele. 
These gift packages consist of a variety of 
maple products attractively packaged. Orders 
are usually received and made up for special 
occasions, particularly for the Christmas sea- 
son. 

Ili{>;h-Klav<n<'<l ami Hish-Densitv Sirup 

To meet ever-increasing demands for high- 
flavored sirup (described on p. 106) for use in 
making some maple-blended table sirups, a con- 
siderable portion of bulk sirup will require high 
flavoring. Most of this will be done by the open 
steam-kettle process or by the new continuous 
process. 

High-density sirup will also need to be made 
to meet consumer demands. The process is 
described on page 105. 

Man iiliK'l lire «(' (',<»iirec>tions 

All well-managed central evaporator plants 
should have a candy kitchen for manufacturing 
confections (fig-s. 134-136). The cost of convert- 
ing standard-density sirup to confections is 
small compared to the selling price of the con- 
fections; confection manufacture is the most 
profitable enterprise of the central plant. The 
principal confections made are maple cream, 




PN-4k:!U 

Figure 13i. — A well-equipped candy kitchen with dehu- 
midifier and air-conditioner is an essential part of a 
central evaporator plant. The candy kitchen furnishes 
employment a major part of the year. 




PN-1831 

Figure 135.— A central evaporator plant must have a 
salesroom for displaying- and selling the products 
manufactured. 




PN^832 

Figure 136.— A large, easily read sign advertising the 
central evaporator plant is essential for directing the 
public to the plant for the purchase of maple products. 



maple candies (soft sugar), block sugar, and 
stirred sugar. 

The candy kitchen of the central plant will be 
in operation from 9 to 12 months of the year. 
The manufacture of confections may use more 
than half the plant's sirup production and will 
provide the largest source of income per gallon 
of sirup. A small central evaporator plant may 
produce more than 4 tons of confections a year. 



128 



AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE 



.Siiniiiiar> 

(1) Theoi-etically, the central evai)orator plant 
is sound economically for both the plant 
investor and the suppliers of sap. 

(2) Locate it on an accessible, hard-surfaced, 
touri.st-traveled road. 

{'.i) The plant need not be larp:e, but the larger 
the plant, the larger the returns. Central 
evaporator plants are readily expanded. 

(4) The most common plant is one using oil 
fuel for the bulk of the sap evaporation 
and high-pressure steam for the last stage 
of the evaporation. 

(5) Utilize automation where jwssible. 

(6) Sap should be purchased on the basis of its 
Brix value and volume or weight. The 
price of sap should be on a sliding scale, 
vai-ying with the " Brix of the sap. 

(7) Standards of production should be set for 
sap producers. 



(8) Sap storage facilities must be adequate to 
handle a maximum day's run from all of 
the sap suppliers. 

(9) Sap tanks should be located in a cool place, 
easily accessible for washing and sanitiz- 
ing. Tanks should be provided with germi- 
cidal lamps to prevent sap deterioration by 
microbial s{X)ilage. 

(10) Bulk storage of sirup can be in large tanks 
protected by germicidal lamps or in 5-gal- 
lon tins or 30-gallon drums. 

(11) Sirup for retail trade should be mixed to 
obtain a standard color and density and 
packaged at 190P F. 

(12) Increased returns from the plant will re- 
sult from extending its use throughout the 
year by manufacturing confections, cus- 
tom-packaging sirup, and preparing gift 
packages of assorted maple products. 



REFERENCES CITED 



(1) Anonymous. 

1975. SAP PRICES. Natl. Maple Syrup Digest 14 
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H. D. 
1957. THE INFLUENCE OF HEAT TREATMENT ON 
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(2) Arnold, E. L. 

1960. using water pumps for gathering ma- 
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(3) BaGGLEY, G. F., and MaCHWART, G. M. 

1947. MAPLE SYRUP MANUFACTURE, USING A 
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(4) Balch, R. T. 

1930. MAPLE SIRUP COLOR STANDARDS. Indus, 
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(5) Bell, R. D. 

1955. costs and returns in producing and 
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STATE. Cornell Univ., Dept. Agr. Econ., A. 
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(6) Betts, H. S. 

1945. MAPLE (ACER SPECIES). U.S. Forest Serv., 
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(7) Blum, B. M., and KOELUNG, M. R. 

1968. VACUUM PUMPING INCREASES SAP YIELDS 
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(8) Bond. A. D. 

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BOSTWICK, E. p. 
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(11) Burns, M., and Personious, C. J. 

1962. using maple sirup. N.Y. (Cornell) Agr. 
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(12) Canada Department of Agriculture. 

1961. maple syrup, sugar, butter, taffy. 
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1960. SOME EVIDENCE OF PREMATURE STOPPAGE 
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1969. TWO AUTOMATIC SIRUP DRAWOFF CON- 
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12 pp. 



MAPLE SIRUP PRODUCERS MANUAL 



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(22) 



(23) 



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(29) 



Cool, B. M. 

1957. an investigation of the effect of some 
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IN A CENTRAL MICHIGAN WOODLOT. (Thesis 
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COSTILOW, R. N., ROBBINS, P. W., SIMMONS, R. J., 
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1962. THE EFFICIENCY AND PRACTICABIUTY OF 
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PELLETS FOR CONTROLLING MICROBIAL 
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Davis, D. R., Hacskaylo, J., Gallander, J., and 
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1962. SUGAR SANDS ARE IMPORTANT PART OF MA- 
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Desilets, D. 

1972. the application of vacuum for maple 
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Dunn, S., and Townsend, R. J. 

1954. PROPAGATION OF SUGAR MAPLE BY VEGE- 
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. 679. 
DYCE, E. J. 

1935. HONEY PROCESS AND PRODUCT. (U.S. Pat- 
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ElCHMEIER, A. H. 

1955. WEATHER AND MAPLE SYRUP. U.S. 
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Energy Control Co. of New York, N.Y. 
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England, G. M., and Enoch, H. T. 

1956. MARKETING VERMONT'S MAPLE SYRUP. Vt. 
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FiLiPic, V. J., Underwood, J. C, and Dooley, C. J. 

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(n. d.l TAP YOUR TREES. Vt. Agr. Ext. Ser., 5 pp. 

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Frank, H. A. 

1962. INFLUENCE OF LOW INCUBATION TEMPERA- 
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NaGHSH, J., Reed, L. L., and WiLLITS, C. 0. 

1959. MAPLE SIRUP. XII. THE EFFECT OF ZINC ON 
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and WiLUTS, C. O. 

1960. MAPLE SIRUP. XIII. STERIUZING EFFECT OF 
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(:30) and WiLLITS, C. 0. 

1961. MAPLE SIRUP. XVII. PREVENTION OF MOLD 
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(31) and WiLLITS, C. O. 

1961. MAPLE SIRUP. XVIII. BACTERIAL GROWTH 
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1963. SWEET SUGAR MAPLES WANTED. Natl. Ma- 
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(33) Marvin, J. W., and Tay'lor, F. H. 

1961. ROOTING GREENWOOD CUTTINGS OF SUGAR 
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U.S. Forest Serv., Northeast. Forest Expt. 
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(34) Greene, M. T., and Marvin, J. W. 

1958. THE WATER CONTENT OF MAPLE STEMS. I. 
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1958. THE WATER CONTENT OF MAPLE STEMS. II. 
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1975. REMOVAL OF BUDDY FLAVOR FROM MAPLE 
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(37) Hubbell, C. 

In.d.l THE ART OF MAKING MAPLE CREAM. 6 pp. 
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(38) Jones, a. r. c. 

1962. plastic tubing or sap buckets. mac- 
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(.39) Jones, C. H., Edson, a. W., and MORSE, W. J. 

1903. THE MAPLE SAP FLOW. Vt. Agr. Expt. Sta., 
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(40) Jones, G. a. 

1961. WE CAN INCREASE SAP \TELDS. MacDonald 
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(41) 

1962. CHEMICALS TO INCREASE SAP Y'lELDS. 
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(42) Jordan, W. K., Kosikowsh, K. V., and March, 

R. P 

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(43) KISSINGER, J. C, and BELL, R. A. 

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130 



AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE 



(44) KOELUNG, M. R. 

1972. VACUUM PRODUCING EQUIPMENT FOR MAPLE 
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(45) KRIEBEL, H. B. 

1957. PATTERNS OF GENETIC VARIATION IN SUGAR 
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56 pp., illus. 

(46) 

1961. FERTIUZATION INCREASES SAP SWEETNESS 
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46 (6): 92-93, illus. 

(47) LainG, F. M., and ARNOLD, E. L. 

1971. USE OF VACUUM IN PRODUCTION OF MAPLE 
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Res. Rpt. MP-64, 17 pp. 

(48) LIGHTHALL, M. T. G., and MARVIN, J. W. 

1960. THE USE OF PLASTIC TUBING IN GATHERING 

MAPLE SAP. Vt. Agr. Expt. Sta. Pam. 32, 11 
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(49) LIGHTHALL, M. T. G., and Marvin, J. W. 

1962. STUDIES ON PIPEUNE SYSTEMS FOR GATH- 
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Agr. Expt. Sta. Misc. Pub. 17, 5 pp. 

(50) Marvin, J. W., and Lighthall, M. T. G. 

1962. EFFECT OF NEW TECHNIQUES ON MAPLE SAP 
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(51) Lamb, A. F., and PersonIUS, C. J. 

1957. USING MAPLE SIRUP. N.Y. (Cornell) Agr. 
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(52) Lento, H. G., Jr., Underwood, J. C, and willits, 

CO. 

1958. BROWNING OF SUGAR SOLUTIONS, n. EF- 
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(53) UNDERWOOD, J. C, and WILUTS, C. O. 

1960. BROWNING OF SUGAR SOLUTIONS. IV. THE 

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756. 

(54) Underwood, J. C., and Willits, c. O. 

I960. BROWNING OF SUGAR SOLUTIONS. V. EF- 
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(55) Little, E. L., Jr. 

1953. check ust of native and naturalized 
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(56) Maroney, R. H. 

1950. TRENDS IN EVAPORATOR DESIGN. Conf. on 
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(57) Marvin, J. W. 

1949. CHANGES IN BARK THICKNESS DURING SAP 
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232, illus. 



(58) and GREENE, M. T. 

1951. TEMPERATURE-INDUCED SAP FLOW IN EX- 
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(59) and GREENE, M. T. 

1959. SOME FACTORS AFFECTING THE YIELD FROM 
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611, 28 pp., illus. 

(60) Meeker, e. W. 

1950. CONFECTIONERY SWEETENERS. Food Tech- 
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(61) M^HOT, J. R., and ROMPRfe, N. 

1953. MAPLE SUGAR INDUSTRY IN QUEBEC. Que- 
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(62) MONEY, R. W., and BoRN, R. 

1951. EQUILIBRIUM HUMIDITY OF SUGAR SOLU- 
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(63) MooRE, H. R., ANDERSON. W. R., and Baker, R. H. 

1951. OHIO MAPLE SYRUP . . . SOME FACTORS IN- 
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(64) MORROW, R. R. 

1952. CULLING SUGAR BUSH FOR LOW-COST PRO- 
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Sta.l 18(1): 7, illus. 



(65) 



1953. 



(66) 



(67) 



(68) 



(69) 



(70) 



(71) 



(72) 



(73) 



BIG TREE CROWNS MEAN CHEAPER SIRUP. 
Farm Res. [N.Y. State Agr. Expt. Sta.] 19(1): 
12. 

EARLY TAPPING FOR MORE QUALITY SIRUP. 
Jour. Forestry 53: 24-25. 

INFLUENCE OF TREE CROWNS ON MAPLE SAP 
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Bui. 916, 30 pp., illus. 

PLASTIC TUBING TESTED FOR MAPLE SAP 
PRODUCTION. Farm Res. [N.Y. State Agr. 
Expt. Sta.] 24: (3), 4-5, illus. 

HARDWOOD FUEL FOR BOILING MAPLE SAP? 
Farm Res. [N.Y. State Agr. Expt. Sta.J 25: 
(4), 2, illus. 

PLASTIC TUBING FOR MAPLE SAP. Farm 
Res. (N.Y. State Agr. Expt. Sta.] 27: (2), 12- 
13. 

RELATIVE VALUES IN MAPLE SIRUP ENTER- 
PRISES. Dept. Mimeo. C-32. 

INFLUENCE OF NUMBER AND DEPTH OF TAP 
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THE APPUCATION OF VACUUM IN SUGAR 
BUSHES. N.Y. State Col. Agr. (Cornell), 
Dept. Conserv., Res. Ser. No. 1, 19 pp. 



MAPLE SIRUP PRODUCERS MANUAL 



131 



(74) NAGHSK], J. 

1953. THE ORGANISMS OF MAPLE SAP: THEIR EF- 
FECT AND CONTROL. (Summary) Second 
Conf. on Maple Prod. (U.S. Agr. Res. Serv., 
East. Util. Res. Br., Philadelphia, Nov. 16- 
18). Rpt. Proc. 2: 48-52. [Processed.] 

(75) REED, L. L., and WILLITS, C. O. 

1957. MAPLE SIRUP. X. EFFECT OF CONTROLLED 
FERMENTATION OF MAPLE SAP ON THE 
COLOR AND FLAVOR OF MAPLE SIRUP. Food 
Res. 22: 176-181. 

(76) and WILLITS, C. O. 

1953. MAPLE SIRUP. VI. THE STERILIZING EFFECT 
OF SUNLIGHT ON MAPLE SAP COLLECTED IN A 
TRANSPARENT PLASTIC BAG. Food Technol. 
7: 81-83, illus. 

(77) and WILLITS, C. O. 

1955. MAPLE SIRUP. IX. MICROORGANISMS AS A 
CAUSE OF PREMATURE STOPPAGE OF SAP 
FLOW FROM MAPLE TAP HOLES. Appl. Mi- 
crobiol. 3: 149-151, illus. 

(78) and WILLITS, C. O. 

1956. TESTING MAPLE SIRUP FOR CREAMING. U.S. 
Dept. Agr. Leaflet 400, 8 pp., illus. 

and WILLITS, C. O. 

1957. MAPLE SIRUP. XI. RELATIONSHIP BETWEEN 
THE TITE AND ORIGIN OF REDUCING SUGARS 
IN SAP AND THE COLOR AND FLAVOR OF MA- 
PLE SIRUP. Food Res. 22: 567-571. 

WILUTS, C. O., and PORTER, W. L. 

1955. MAPLE SIRUP. VIII. A SIMPLE AND RAPID 
TEST FOR THE ANALYSIS OF MAPLE SIRUP 
FOR INVERT SUGAR. Food Res. 20: 138-143. 

WILLITS, C. O., Porter, W. L., and White. J. 

W., Jr. 

1956. MAPLE-HONEY SPREAD AND PROCESS OF 
MAKING THE SAME. U.S. Patent No. 
2,760,870. 

New Hampshire Maple Producers Associa- 
tion Inc. 

1962. new HAMPSHIRE MAPLE SYRUP— ITS CARE 

AND USE. 15 pp. Concord. (Rev.) 
New York State Department of Agriculture 

AND Markets. 
1956. new YORK state official standards, 
definitions, rules and regulations for 

MAPLE products. EFFECTIVE APRIL 1.1, 
1941. N.Y. State Bur. Mkts. .300—5/16/56, 
pp. [Processed.] 

Paine, H. S. 

1924. constructive chemistry in relation to 

CONFECTIONERY MANUFACTURE. Indus, 
and Engin. Chem. 16: 51.3-517. 

1929. CANDY MAKERS CONTROL SOFTENING ( 

CREAM CENTERS. Food Indus. 1: 200-202, 

illus. 
Pasto, J. K., and Ta-^-LOR, R. D. 
1962. ECONOMICS OF THE CENTRAL EVAPORATOR 

IN MAPLE SYRUP PRODUCTION. Pa. Agr. 

Expt. Sta. Bui. 697, 28 pp. 



(79) 



(80) 



(81) 



(82) 



(83) 



(84) 



(85) 



(87) Phillips, G. W. M., and Homiller, R. P. 

1953. oil firing FOR THE MAPLE SIRUP EVAPO- 
RATOR. U.S. Bur. Agr. and Indus. Chem. 
AIC>-3.58, [10] pp., illus. [Processed.] 

(88) Pollard, J. K., Jr., and Sproston, T. 

1954. nitrogenous constituents of sap EX- 
UDED FROM THE SAPWOOD OF ACER SAC- 
CHARUM. Plant Physiol. 29: .360-364, illus. 

(89) Porter, w. L., Buch, m. L., and WILLITS, c. O. 

1951. MAPLE SIRUP, ni. preliminary STUDY OF 

the nonvolatile acid fraction. Food 
Res. 16: .338-341. 

(90) Buch, M. L., and WiLUTS, C. O. 

1952. MAPLE SIRUP. IV. effect OF HEATING 
SIRUPS under CONDITIONS OF HIGH TEM- 
PERATURE and LOW WATER CONTENT: SOME 
PHYSICAL AND CHEMICAL CHANGES. Food 
Res. 17: 475^81, illus. 

(91) HOBAN, N., and WILLITS, C. O. 

1954. CONTRIBUTION TO THE CARBOHYDRATE 
CHEMISTRY OF MAPLE SAP AND SIRUP. Food 
Res. 19: 597-602, illus. 

(92) ROBBINS, P. W. 

1947. THE COST OF MAKING MAPLE SIRUP. Mich. 
Agr. E.xpt. Sta. Quart. Bui. 29: 188-189. 



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(94) 



1948. POSITION OF TAPPING AND OTHER FACTORS 
AFFECTING THE FLOW OF MAPLE SAP. 
[Unpublished Master's Thesis. 0>py on file 
in library, Mich. State Univ., East Lansing.) 

1953. FACTORS INFLUENCING THE PRODUCTION OF 
HIGH QUAUTY MAPLE SAP. (Summary) Sec- 
ond Conf. on Maple Prod. (U.S. Agr. Res. 
Serv., East. Util. Res. Br., Philadelphia, Nov. 
16-18). Rpt. Proc. 2: 34-36. [Processed.] 

1960. THE YIELD OF MAPLE SAP PER TAPHOLE. 
Mich. Agr. Expt. Sta. Quart. Bui. 43: 142- 
146. 



[n. d.] INFLUENCE OF TAPPING TECHNIQUES ON 
MAPLE SAP YIELDS. Mich. Agr. Expt. Sta. 
Farm Sci. Res. Rpt. 28, 3 pp. 

(97) SanfoRD, M. 

1962. BorUNG SAP WITH STEAM. 4 pp. Little Uen- 
esee, N.Y. [Unnum. Mimeo.] 

(98) Sattler, L., and Zerban, F. W. 

1949. unfermentable reducing substances in 
MOLASSES. Indus, and Engin. Chem. 41: 
1401-1406, illus. 

(99) SCARBOROUGH, N. F. 

1932. THE CRYSTALUSATION OF CONFECTIONERY. 
Food Technol. [London] 2: 1—1. illus. 
(100) SCHNEIDER, I. S., Frank, H. A., and WILLITS, C. 0. 

1960. MAPLE SIRUP. XIV. ULTRAVIOLET IRRA- 
DIATION EFFECTS ON THE GROWTH OF SOME 
BACTERIA AND YEASTS. Food Res. 25: 654- 
662. 



132 



AGRICULTURE HANDBOOK VU, U.S. DEPT. OF AGRICULTURE 



(101) SCHUETTE, H. A., and SCHUETTE, S. C. 

1935. MAPLE SUGAR: A BIBLIOGRAPHY OF EARLY 
RECORDS. Wis. Acad. Sci., Art.s Letters 
Trans. 29: 209-236. 

(102) SHENEMAN, J. M., and COSTlU)W, R. N. 

1959. IDENTIFICATION OF MICROORGANISMS FROM 
MAPLE TREE TAPHOLES. Food Res. 24; 146- 
151. 

(103) COSTILOW, R. N., ROBBINS, p. W., and DOUG- 
LASS, J. E. 

1959. CORRELATION BETWEEN MICROBIAL POPU- 
LATIONS AND SAP YIELDS FROM MAPLE 
TREES. Food Res. 24: 152-159. 

(104) SIPPLE, L., WILUTS, C. O.. and WINCH, F. E., JR. 
1963. ARCHES AND BURNERS FOR OIL-FIRED MA- 
PLE SAP EVAPORATORS. U.S. Agr. Res. 
Serv. ARS 73^0, 14 pp., illus. 

(105) Smith, H. C. 

1971. sap volume flow as influenced by tub- 
ing diameter and slope percent. u.s. 

Forest Serv., Northeast. Forest Expt. Sta. 
Res. Note NE-137, 6 pp. 

(106) and GIBBS, C. B. 

1970. COMPARISON OF VACUUM AND GRAVITY SAP 
FLOWS FROM PAIRED SUGAR MAPLE TREES. 
U.S. Forest Serv., Northeast. Forest Expt. 
Sta. Res. Note NE-122, 4 pp. 

(107) Snyder, C. F.. and Hammond, L. D. 

1946. WEIGHTS PER UNITED STATES GALLON AND 
WEIGHTS PER CUBIC FOOT OF SUGAR SOLU- 
TIONS. I U.S.I Natl. Bur. Standards Cir. 457, 
28 pp. [Processed.! 

(108) Sproston, T., Jr., and LANE, S. 

1953. MAPLE SAP contamination AND MAPLE 
SAP BUCKETS. Vt. A}jr. Expt. Sta. Pam. 28, 4 
pp. 

(109) and SCOTT, W. W. 

1954. VALSA LEUCOSTOMOIDES, THE CAUSE OF 
DECAY AND DISCOLORATION IN TAPPED 
SUGAR MAPLES. Phytopathology 44: 12-13, 
illus. 

(110) STEVENSON, D. D., and BaRTOO. R. A. 

1940. COMPARISON OF THE SUGAR PER CENT OF 
SAP IN MAPLE TREES GROWING IN OPEN AND 
DENSE GROVES. Pa. State Forest Sch. Res. 
Paper 1, 3 pp. [Processed.! 

(111) Strolle, E.g., Cording, J., Jr., and Eskew, R. K. 

1956. AN ANALYSIS OF THE OPEN-E'AN MAPLE- 
SIRUP EVAPORATOR. U.S. Agr. Res. Serv. 
ARS 73-14, 14 pp., illus. 

(112) TAYLOR, F. H. 

1956. VARIATION IN SUGAR CONTENT OF MAPLE 
SAP. Vt. Agr. Expt. Sta. Bui. 587, 39 pp. 

(113) Trenk, F. B., and McNall, P. E. 

1954. COSTS OF PRODUCING MAPLE SYRUP IN Wl.s- 
CONSIN. IWis. Agr. Expt. Sta.! 6 pp., il- 
lus. [ Processed. 1 

(114) TRESSLER, C. J., and ZIMMERMAN, W. 1. 

1942. THREE YEARS' OPERATION OF AN EXPERI- 
MENTAL SUGAR BUSH. N.Y. State (Geneva) 
Agr. Expt. Sta. Bui. 699, 24 i)p.. illus. 



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Underwood, J. C. 

1963. QUICK TEST FOR "BUDDY" FLAVOR IN MAPLE 
SIRUP. U.S. Agr. Res. Serv. ARS 7.3-12, 4 pp. 

EFFECT OF HEAT ON THE FLAVORING COM- 
PONENTS OF MAPLE SIRUP: A PRELIMINARY 
STUDY BY GAS CHROMATOGRAPHY. Jour. 
Food Sci. 36: 228-230. 

and FlUPIC, V. J. 

GAS CHROMATOGRAPHIC IDENTIFICATION OF 
COMF'ONENTS IN MAPLE SIRUP FLAVOR EX- 
TRACT. Assoc. Off. Agr. Chem. Jour. 46: 
334-337. 



(118) 



(119) 



(120) 



(121) 



(122) 



(123) 



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(125) 



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(127) 



and LENTO, H. G. 

1960. SOME PHYSICAL CHARACTERISTICS OF THE 
2,4-DINITROPHENYLHYDRAZINE AND SEMI- 
CARBAZIDE DERIVATIVES OF THREE-CARBON 
CARBONYLS. Anal. Chem. 32: 1656-1658. 

LENTO, H. G., Jr., and WiLLITS, C. O. 

1956. TRIOSE COMPOUNDS IN MAPLE SIRUP. Food 

Res. 21: 589-597. 
Lento, H. G., Jr., and Willits, C. O. 

1959. BROWNING OF SUGAR SOLUTIONS. 3. EF- 
FECT OF PH ON THE COLOR PRODUCED IN 
DILUTE GLUCOSE SOLUTIONS CONTAINING 
AMINO ACIDS WITH THE AMINO GROUP IN 
DIFFERENT POSITIONS IN THE MOLECULE. 
Food Res. 24: 181-184. 

and WILUTS, C. O. 

1959. SCALE IN MAPLE-SIRUP EVAPORATORS- 
HOW TO REMOVE IT. U.S. Dept. Agr. Inform. 
Bui. 203, 4 pp. 

Willits, C. O., and Lento, H. G. 

1961. BROWNING OF SUGAR SOLUTIONS. VI. ISO- 
LATION AND CHARACTERIZATION OF THE 
BROWN PIGMENT IN MAPLE SIRUP. Jour. 
Food Sci. 26: 397-400. 

WILUTS, C. O., and LENTO, H. G. 

1961. MAPLE SIRUP. XVI. ISOLATION AND IDEN- 
TIFICATION OF COMPOUNDS CONTRIBUTING 
TO THE FLAVOR OF MAPLE SIRUP. Jour. 
Food Sci. 26: 288-290. 

United States Department of Agriculture. 

1949. trees; the yearbook of agriculture, 

1949. 944 pp., illus. Washington, (Various 
references to maple sugar.) 

1952. AGRICULTURAL STATISTICS 19!-.2. 876 pp. 
Washington. 

1956. AGRICULTURAL STATISTICS ig.'io. 610 pp. 
Washington. 

1963. AGRICULTURAL STATISTICS 19fi2. 741 pp. 
Washington. 



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1972. AGRICULTURAL STATISTICS 197 
Washington. 



759 pp. 



MAPLE SIRUP PRODUCERS MANUAL 



133 



(129) United States Department of Agriculture, 

Consumer and Marketing Service. 
1967. united states standards for grades of 

TABLE MAPLE SIRUP. (Effective May 24, 
1967). 2 pp. (Processed.! 

(130) UNITED States Food and Drug Administra- 

tion. 
1962. FOOD additives. Fed. Register 27: 1554. 

(130a) 

1974. FOOD LABEUNG. Fed. Register 39: 20882. 

(131) Vermont Department of Agriculture. 

1950. vermont maple syrup grading and 
marketing law, effective march 1, 
ig.'iO. Vt. Dept. Agr., Div. Mkts. Cir. 14, 16 
pp. 

(132) Vermont Development Department and Ver- 

mont Department of Agriculture. 

1962. VERMONT maple sirup and SUGAR. 16 pp., 
illus. Montpelier, Vt. (Rev.) 

(133) Wasserman, a. E. 

1963. microbiology and sanitation in the 
sugar bush and sugar house. u.s. agr. 
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1964. 



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1962. 



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1961. 



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MAPLE SIRUP. XXII. CONTROLLED FER- 
MENTATION OF BUDDY MAPLE SIRUP. Food 
Techno!. 18: 142-145. 
UNDERWOOD, J. C, and WiLUTS, C. O. 

FLUFFED MAPLE PRODUCTS — A NEW USE 
FOR MAPLE SIRUP. U.S. Agr. Res. Serv. 
ARS 73-39, 6 pp. 
and WILLITS, C. O. 

MAPLE SIRUP. XX. CONVERSION OF 
"BUDDY" MAPLE SAP INTO NORMAL MAPLE 
SIRUP. Food Technol. 15: 438-439. 
- and WILLITS, C. O. 
In. d.l PREPARATION OF MAPLE SIRUP FROM 

BUDDY SAP. Filed in Patent Office 10/17/61 

as Serial No. 145,783. (Pat. pending.) 

(138) WEBER, P. D. 

1956. WISCONSIN MAPLE PRODUCTS; PRODUCTION 
AND MARKETING. Wis. Dept. Agr. Bui. 335, 
48 pp., illus. 

(139) Whitby, G. S. 

1936. manufacture of maple products of in- 
TENSE FLAVOR. (U.S. Patent No. 
2,054,873.) U.S. Patent Office, Off. Gaz. 470: 
787. 

(140) WiLUTS, C. 0. 

1951. CROPS FROM THE MAPLE TREES. U.S. Dept. 
Agr. Ybk. Separate 2208. [Reprint from 
Yearbook of Agriculture, 1950-1951: 316- 
321.) 



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1953. SOME CHANGES THAT SAP UNDERGOES IN A 
CONTINUOUS ATMOSPHERIC EVAPORATOR. 
Second Conf. on Maple Prod. (U.S. Agr. Res. 
Serv., East. Util. Re.s. Br., Philadelphia, Nov. 
16-18). Rpt. Proc. 2: 30-32. [Processed.] 

MAPLE AIDS IN BETTER LAND USE PRO- 
GRAM. Natl. Maple Syrup Digest 1 (3): 8, 10. 



(143) 

1962. MODERNIZATION OF THE MAPLE SYRUP IN- 
DUSTRY. Natl. Maple Syrup Digest 1 (1): 6- 
7. 

(144) Frank, H. A., and Bell, R. A. 

1959. CLEANING PLASTIC EQUIPMENT USED IN 
HANDLING MAPLE SAP. U.S. Agr. Res. Serv. 
ARS 73-23, 12 pp. 

(145) Frank, H. a., and Underwood, J. C. 

1960. MAKING HIGH-DENSITY, HIGH-FLAVORED 
MAPLE SIRUP. U.S. Agr. Res. Serv. ARS 73- 
26, 8 pp. 

(146) Frank, H. A., and Underwood, J. C. 

1960. MEASURING THE SUGAR IN MAPLE SAP AND 
SIRUP. U.S. Agr. Res. Serv. ARS 73-28, 21 
pp. 

(147) Frank, H. A., and Underwood, J. C. 

1961. filtration of maple SIRUP. Jour. For- 
esti-y 59: 112-113. 

(148) and PORTER, W. L. 

1950. MAPLE SIRUP. II. A NEW HIGH-FLAVORED 
MAPLE SIRUP. U.S. Bur, Agr. and Indus. 
Cheni. AIC-269, 3 pp. 

(149) and PORTER, W. L. 

1955. PRODUCTION OF MAPLE SUGAR PRODUCTS 
HAVING ENHANCED FLAVOR. (U.S. Patent 
No. 2,715,581.) 

(150) Porter, W. L., and Buch, M. L. 

1952. MAPLE SIRUP. V. FORMATION OF COLOR 
DURING EVAPORATION OF MAPLE SAP TO 
SIRUP. Food Res. 17: 482-186, illus. 

(151) SHOLETTE, W. p., and UNDERWOOD, J. C. 

1958. THE DETERMINATION OF MALIC ACID IN MA- 
PLE SIRUP BY AN ION EXCHANGE PROCE- 
DURE: AN ADAPTATION OF THE GOODBAN 
AND STARK METHOD. Assoc. Off. Agr. Chem. 
Jour. 41: 658-662. 

'152) and SiPPLE, L. 

1961. THE USE OF PLASTIC TUBING FOR COLLECT- 
ING AND TRANSPORTING MAPLE SAP. U.S. 
Agr. Res. Serv. ARS 73-35, 19 pp., illus. 

(153) and UNDERWOOD, J. C. 

1961. METHODS OF ANALYSIS FOR MAPLE SIRUP: 
USDA COLOR COMPARATOR. Assoc. Off Agr. 
Chem. Jour. 44: 330-333. 

(154) Underwood, J. C, and Lento, H. G. 

1959. PROCESS FOR MAKING MAPLE PRODUCT OF 
INTENSIFIED MAPLE FLAVOR. (U.S. Patent 
No. 2,895,833.) 

(155) Underwood, J. C, Lento, H. G., Jr., and 

RICCIUTI, C. 
1958. browning of SUGAR SOLUTIONS. I. EF- 
FECT OF PH AND TYPE OF AMINO ACID IN 
DILUTE SUGAR SOLUTIONS. Food Res. 23: 
61-67. 
(1.56) Winch, F. E., Jr. 

in. d.l bacterial control for higher quality 

SAP. Inform. Sheet. 
(157) and MORROW, R. R. 

1962. PRODUCTION OF MAPLE SIRUP AND OTHER 
MAPLE PRODUCTS. N.Y. (Cornell) Agr. Ext. 
Bui. 974, 40 pp. (Rev.) 



134 



AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE 

SUPPLEMENTAL READING 



Anonymous. 

1940. maple sugar [sirup] in cigarettes. can- 
ada Lumberman 60 (8): 12. 

1942. CANADIAN MAPLE HARVEST. Jour. Forestry 
40: 806. _ 

ANDERSON, W. R., and METEER, J. W. 

1948. MAKING FARM FORESTRY PAY. Ohio Forestry 
Assoc. News Bui. 1 (2): 111-2. 

ASHE, W. W. 

1897. THE POSSIBIUTIES OF A MAPLE SUGAR INDUS- 
TRY IN WESTERN NORTH CAROLINA. N.C. 
Geol. Survey, Econ. Papers 1, 34 pp., illus. 
BARRACLOUGH, K. E. 

1952. MAPLE SYRUP AND SUGAR PRODUCTION IN 
NEW HAMPSHIRE. N.H. Univ. [Agr.) Ext. Bui. 
103. 28 pp., illus. 
BATES, F. J., and BeARCE, H. W. 

1918. NEW BAUM6 SCALE FOR SUGAR SOLUTIONS. 
[U.S.] Natl. Bur. Standards Technol. Papers 
115, 11 pp. 
BERKSHIRE Pioneer Maple Producers' Association. 

In. d.l MASSACHUSETTS PURE MAPLE SYRUP. 7 pp. 
Ashfield, Mass. 
Bryan, A. H. 

1910. MAPLE-SAP SIRUP: ITS MANUFACTURE, COM- 
POSITION, AND EFFECT OF ENVIRONMENT 
THEREON. U.S. Bur. Chem. Bui. 134, 110 pp, 
illus. 
Hubbard, W. F., and Sherwood, s. F. 

[1923.1 PRODUCTION OF MAPLE SIRUP AND SUGAR. 
U.S. Dept. Agr. Farmers' Bui. 1366, 35 pp., 
illus. (Rev. 1937.) 

StraUGN, M. N., Church, C. G., and others. 

1917. MAPLE SUGAR: COMPOSITION, METHODS OF 
ANALYSIS, EFFECT OF ENVIRONMENT. U.S. 
Dept. Agr. Bui. 466, 46 pp., illus. 
CHITTENDEN, A. K., and ROBBINS, P. W. 

1930. THE COST OF MAKING MAPLE SYRUP. In The 
Farm Woodlot in Michigan, Mich. Agr. Expt. 
Sta. Spec. Bui. 196, p. 14. 
CHRISTOWE, M. 

1946. GREEN MOUNTAIN SAP. Farm Quart. 1 (4): 38- 
43, 134-1.35, illus. 
COLLINGWOOD, G. H., and COPE, J. A. 

1938. MAPLE SUGAR AND SIRUP. N.Y. Agr. Col. (Cor- 
nell) Ext. Bui. 397, .32 pp., illus. (Rev. 1944.) 
Cope. J. A. 

1949. DEPTH OF TAPPING IN RELATION TO YIELD OF 
MAPLE SAP. Jour. Forestry 47: 478-480. 

1949. MAPLE SIRUP AND SUGAR. N.Y. Agr. Col. (Cor- 
nell) Ext. Bui. 397, .32 pp., illus. (Rev.) [First 
printed 1938; the revision reprinted 1952.1 
Dambach, C. a. 

1944. comparative productiveness of adjacent 
grazed and ungrazed sugar-maple 
WOODS. Jour. Forestry 42: 164-168. illus. 



Dansereau, p. 

1944. L'INDUSTRIE DE L'ERABLE. Universite de 
Montreal, Institut de Biologie (Secretariat de 
la Province de Quebec, Service de Biogeogra- 
phie). 44 pp., illus. [Quebec. I [Processed.] 
Edson, H. a., Jones, C. H., and Carpenter, C. W. 

1912. MICRO-ORGANISMS OF MAPLE SAP. Vt. Agr. 
Expt. Sta. Bui. 167: [3211-610, illus. 
Fabian, F. W., and Buskirk, H. H. 

1935. AEROBACTER AEROGENES AS A CAUSE OF 
ROPINESS IN MAPLE SIRUP. Indus, and Engin. 
Chem., Indus. Ed., 27: .349-450. 
Finlay, M. C. 

11934.] our american maples and some others. 
19 pp., illus. New York. 

GILMAN, W. 

1949. MAPLE— THE MYSTERY TREE. 
42: 119-122, illus. 
GOING, M. 

1917. 



Nature Mag. 



Canad. For- 



IN THE MAPLE SUGAR SEASON. 

estry Jour. 13: 992-994, illus. 
GROSE, L. R. 

1920. MAPLE SUGAR IN COLONIAL TIMES. Amer. 

Forests 26: 689-690. 
Hayward, F. W. 

1946. THE STORAGE OF MAPLE SIRUP. N.Y. State 
Agr. Expt. sta. Bui. 719, 8 pp., illus. 

and PedeRSON, C. S. 

1946. SOME FACTORS CAUSING DARK-COLORED MA- 
PLE SIRUP. N.Y. State Agr. Expt. Sta. Bui. 
718, 14 pp.. illus. 
Herbert, P. A. 

1924. the weather and MAPLE SUGAR PRODUC- 
TION. Mich. Agr. Expt. Sta. Quart. Bui. 7: 60- 
62, illus. 
Herr, C. S. 

1938. maple syrup and sugar production in 
NEW HAMPSraRE. N.H. Univ. lAgr.l Ext. Bui. 
52, 20 pp., illus. 
Hills, J. L. 

1904. the maple sap flow. Vt. Agr. Expt. Sta. 
Bui. 105: [1931-222, illus. 
Hitchcock, J. A. 

1928. economics of the farm manufacture of 
maple syrup and sugar. Vt. Agr. Expt. Sta. 
Bui. 285. 96 pp., illus. 



1929. COST AND PROFIT IN THE SUGAR ORCHARD. 
Agr. Expt. Sta. Bui. 292, 19 pp., illus. 



1937. 



Vt. 



THE GRAZING OF MAPLE SUGAR ORCHARDS. 
Vt. Agr. Expt. Sta. Bui. 414, 14 pp., illus. 
HUFFMAN, R. E., DeVault, S. H., and Coddington, J. W. 
1940. an economic study of THE MAPLE PRODUCTS 
industry in GARRETT COUNTY, MAR^XAND. 
Md. Agr. Expt. Sta. Bui. 431. pp. 16.5-215, illus. 



MAPLE SIRUP PRODUCERS MANUAL 



135 



HuTCHiNs, Mrs. H. 

1900. PIONEERING |IN MICHIGAN) — GATHERING SAI' 
AND GOING TO MILL. (A poem.) In (Mich. 
Hist. Comm.,1 [Mich.) Hist. Collect. (1897-9S) 
28: 638-640. (Collections and Researches 
made by Michigan Pioneer and Historical Soci- 
ety.) 
Jones, c. H. 

1938. the exclusion of lead from maple sap. 

(PROGRESS REPORT.) Vt. Agr. Expt. Sta. Bui. 
439, 7 pp. 
and Bradlee, J. L. 

1933. the carbohydrate CONTENTS OF THE MAPLE 
TREE. Vt. Agr. Expt. Sta. Bui. 358, 147 pp., 
illus. 

Kelley, M. C. 

1933. SAP, SUGAR AND SHEEPSKINS. Amer. Forests 
39: 114-115, 144, illus. 

1936. SAVING THE SUGAR ORCHARD. Amer. Forests 
42: 221, 242, illus. 

MclNTYRE, A. C. 

1932. THE MAPLE PRODUCTS INDUSTRY OF PENN- 
SYLVANIA. Pa. Agr. Expt. Sta. Bui. 280, 47 
pp., illus. 

McKay, A. W. 

1922. MARKETING VERMONT MAPLE-SAP PRODUCTS. 
Vt. Agr. Expt. Sta. Bui. 227, 48 pp., illus. 

Marvin, J. W., and Erickson, R. O. 

1956. A STATISTICAL EVALUATION OF SOME OF THE 
FACTORS RESPONSIBLE FOR THE FLOW OF SAP 
FROM THE SUGAR MAPLE. Plant Physiol. 31: 
57-61. 

[Maryland University Agricultural Extension 
Service and Garrett County Maple Producers 
Association.) 

1931. MAPLE SUGAR AND SIRUP RECIPES. Md. Univ. 
[Agr.l Ext. Cir. 87, 9 pp. 

Moore, H. R., Baker R. H., and Diller, O. D. 

1948. THE FARM SUGAR BUSH. Ohio Farm and 
Home Res. [Ohio Expt. Sta.[ 33 (251): 40-45, 
illus. 
Morrow, r. r. 

1952. consistency in sweetness and flow of 
MAPLE SAP. Jour. Forestry 50: 130-131. 

MURPHEY, F. T. 

1937. THE MAPLE SYRUP CROP. Pa. State Col. Ext. 
Cir. 186, 28 pp., illus. 

1947. MAKING MAPLE SYRUP. Pa. State Col. Ext. Cir 
310, 36 pp., illus. 

Nearing, H., and NEARING, S. 

[1950.1 THE MAPLE SUGAR BOOK. 271 pp., illus. New 
York and Toronto. 
ORMSBEE, C. O. 

1920. EVERY STEP IN MAPLE SUGAR MAKING. Rural 
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